My cat had bloody diarrhea and we suspect it may have to do with Evo treats.

 Last weekend my cat Ozzy was staying in a boarding facility for cats, and as usual, I brought his own canned food and some Evo treats(little less than ½ bag), so he can enjoy his favorite treats and not to be so stressed out  away from home .I didn’t know back then about the salmonella problems in Natura’s foods. When I read about Natura’s recall of various products and saw that those treats were in the list too I was very worried, but it was too late to do something and we were on our way back home. So I could only hope that my kitty was OK and the treats weren’t contaminated!

  And he was perfectly fine for the first two days; the only thing I was concerned about was that I didn’t see any poop yet.  But he is going outside for walks on the leash every single day with my husband or my kids, and sometimes he is doing his business outside in the fresh air.

  After two days being at home he had a very stinky soft poo, and since then (Wednesday), he had soft stools and a lack of appetite. I was offering him boiled chicken, and was adding pumpkin powder to his wet food; he was showing no interest. His activity level is the same and he is not acting strange or out of ordinary.

  Today in the morning I saw blood in his stool and immediately took him to the vet , where he was given SQ fluids with vit. B Complex and B-12 and was prescribed antibiotic Metronidazole. We brought with us a stool sample, so they could run a test to see if it has salmonella.

  So the results are going to be in few days, and I hope it’s not salmonella and nothing very serious, so my sweet boy will get well soon.

I hope it's not Salmonella too and that he didn't pick up a bug while being boarded (though if he has to have something wrong I hope it's a bug). The good part is it sounds like you did everything exactly right by monitoring his stools and taking him in at the first sign of trouble (and by taking a stool sample with you). 

Until you get the results back you could try him on a diet of white rice and canned baby food (or boiled chicken if you prefer). If you do use the canned be certain it's a pure meat formula with no onions or garlic in it. If he has an upset tummy he may prefer the consistency of the baby food to boiled chicken but that's just more of a personal preference. 

When I use this recipe I do 50% white rice (you can use plain old Minute rice) to 50% baby food. Then I add a little warm water just to increase the fluid intake. The starch in the rice is good for stopping the diarrhea, while the baby food provides at least a basic level of protein and water. They can't survive on it for a long period of time as the essential vitamins and minerals are lacking but I have found it's great for a few days to give the tummy a rest and let whatever bug it is run it's course. Even if he isn't having a lot of soft stool he may just need a few days of a bland diet (like we humans need when we don't feel well). 

Even though you have already taken him in and his activity level is normal keep a close eye on him. In addition to your other concerns about what it could be you need to watch him closely to make sure he's not dehydrated. You can test his hydration level by pulling up his scruff (the fur on the back of his neck). In a hydrated cat it will snap back down. If it is slow to do so or "tents" then he may need another dose of SubQ's. If you see this or if he becomes lethargic or stops eating and drinking entirely take him back to the vet ASAP. If he If they are closed go to the nearest after hours/ER vet. 

All my vibes that whatever he has is very treatable and that he's continues to stay active. 

EB24 gave a great answer. I just wanted to add that in case it does not clear up , or happens again, one possibilty is inflammatory bowel disease. Sometimes that can be trigggered by the cat developing a sort of allergic reaction to some ingredient in food, and then the cat needs to change to some kind of food they are not used to. The internal medicine specialist who saw my cat recommended a canned grain free food with the meat being venison, rabbit or duck -- as long as it was something he was not already used to. Natures Variety Instinct has those, and my cat was helped a lot by switching to their venison cat food . Then it was even better when I put him on the raw frozen version of it for about half his diet. He was OK as long as he stayed on that diet. Hopefully your cat will soon be feeling well.

 Thank you, for your wishes, good vibes and valuable advice.

 Ozzy is doing much better since yesterday. His normal diet is grain-free wet and also raw, but when he got sick he refused to eat his canned food and I was hesitant to offer him raw meat.  So we bought 2 cans of Hill’s I/D from the vet office to entice him to eat something (it’s full of by-products and has a strong smell, which is so appealing to cats). He is eating OK, not as well as normal. Also I gave him some chicken baby food, which he likes a lot. He isn’t pooping yet, but peed twice, which is good.

You've been given great advice already.

I do want to add this, as scary as it looks, blood in stool is caused by many things, including eating food/too many treats even, eating something that upset her intestines causing mild inflammation and bleeding. This is not a recurring thing though, and shouldn't be seen more than a time or two.

I especially thought because of her lack of having any bm's the first 2 days, that perhaps it is simply this. If his tests are neg, chances are his system had a temporary upset