Rust-colored blotch in cat litter; blood or just poop?

So I've had an...interesting couple of years.

It has been two years since I lost my first cat, Snowball. And then this stray kitten came along who had no one in its life. Now that little guy's named Rascal and has lived with me and my mom for two yeas now. And so far we've had to keep him in for six months due to a rabies quarantine (he doesn't have rabies, we just have to keep him in for six months total (Only two months to go!) because we brought him in after the neighbors' cat attacked him...again). So now we've turned a mostly outdoor cat into an indoor cat and even built him a small enclosure for him to go in outside.

But what has me concerned is earlier tonight, I went to change his litter box and noticed this rust-colored blotch about the size of my index finger near the side of his box. It wasn't wet or anything (though it's not like I touched it, but it did look dry). It was a finger-sized rust-colored blotch of litter.

He seems to be playing normally and is still quite hyperactive, he doesn't seem to be having any trouble going to to the bathroom (I know this because I watched him while he went about ten minutes ago, and then he rubbed his butt along the carpet), and even though he's being extremely picky about his food and is eating slightly less than he normally does, he's still eating quite a bit. Also, I would show a photo but my mother finished changing the litter box before i could take a photo.

Is there a possibility that it could have been blood? I ask because even though he's two years old, well, let's just say that I've become more cautious (and perhaps paranoid) after I lost Snowball. So...does this sound serious? Or am I just being too paranoid?

Could be blood from his urine. I would monitor and take to the vet within a few days. Better safe than sorry.

When you watched him go to the bathroom, I'm assuming he pooped since he then "rubbed his butt along the carpet".  THAT action is not normal for a cat.  Could be he is having issues with constipation OR  his anal glands.  Have you noticed him licking himself more than normally on his back end?  Or when you watched him go, was he straining more than normal?  If a cat is constipated, sometimes they will bleed a little bit and that could be what you saw, mixed in with the litter.  

If you can determine if he's constipated by watching for signed of straining, or even by checking his poop...is it extremely hard when it first comes out.  Does he sometimes appear to be pooping in areas outside the litterbox but producing nothing.  That is also a sign of constipation (at it's worst).  To help alleviate it if it seems to be that, you can try giving him a little bit of canned plain pumpkin (1 teaspoon 3 times per day), or increase his water intake...I add at least 2 tablespoon of filtered water to every meal of wet food for my guys), or try giving him some slippery elm bark.   This thread might help you with that:  http://www.thecatsite.com/t/270597/slippery-elm-bark-wet-food-managing-constipation

If it's anal glands, they might need to be expressed, something best done by a Vet unless you know what you are doing.