My cat has a weird mark on his face

My cat Milo has a mark on his face, spanning his left lip. It's this weird reddish/brownish mark and it's a little scabby. Milo is a white flame point cat, so it's definitely not developing coloration. It doesn't seem to bother him and it's not swollen, but I'm worried that it might be something serious. My roommate recently got a puppy, and they've had brief, unhappy contact, but no injuries or anything. Could it be from the dog? This is a picture of the mark. It's bad lighting, I know, but Milo is a stubborn kitty and this was the best I could do. Does anyone have any ideas what it could be?

I can't see it very well. Does he goes outside or do you have any other cats? If so, do you know if he fights sometimes?

Could it be an abscess?
Does it hurt when you're touching it and how does it feels like when you're touching it? (soft, hard etc?)

It did have a few black specs. I thought they were fleas at first. I didn't know cats could get acne. I'll have to look at it closer.

He doesn't go outside, but he was a stray. I've had him for 2 months now though. When I touch it, it's not hard or swollen. It's just this weird thing on his face. Milo doesn't seem to be pained by it. He just gets annoyed that I'm messing with his face.