I don't really get the point of delaying the reveal to his friends.
99% of demon society doesn't even seem to know what the fuck a human is, it's not like they hate them or anything, but I get not exposing it publicly because a human being in Hell would spark chaos, specially for grandpa who would get in big trouble. But his friends clearly aren't going to give a fuck. If anything they would be more hurt by him keeping it a secret and this chapter kinda dealt with that potential drama already.
Why not just tell them? Other people already found out anyway.
Extremely late to this, but since I haven't seen anyone mention my perspective: Basically, Iruma is not scared of the demons eating him when they find out.
He's just scared that he won't be able to stay with everyone if they find out he's a human. Think back to the Harvest Festival: what was Iruma's trauma, aside from his parents showing up? It was his friends treating him like a stranger because he's a human. Obviously he knows that his friends are not the kind of people who would say/do that kind of thing, but he's
terrified. That's why he can't bring himself to tell them, not some silly reason like "Oh no I'll be eaten if they find out".
If you're still not convinced, I recommend rereading
Ch. 123, it shows precisely what Iruma fears the most (quite literally). Even though he does end up overcoming the illusion, it doesn't mean his fears are gone.