It's a smart idea to run tests like that and see how the world behaves to new introductions to it. Izuku has been doing similar himself, trying to keep notes where he can while also talking with others to see what things they have learned that he might have missed. This is going to be added to it, for sure.

"Interesting...I wonder what it's using to keep burning, if it doesn't burn the things it catches onto. Just oxygen, maybe?"

Normally that wouldn't be enough- fire needs kindling to keep going, after all- but it's not like this place really cares about logic. As for Bowser's mention of his fire breathing not working, Izuku at least has some more familiarity with that.

"From what I've been able to tell, from my own experience and asking other people, no powers work right now. My friend Kacchan can make explosions with his hands, and that's not working for him either."