He snapped and was rude, and that was wrong, but I can see why he was disappointed, and the OPs attitude doesn't help.
If I inadvertently screw up someone else's plans, I apologise. Its the right thing to do.,whereas the OP seems to genuinely not care about this and is rather confrontational.
Its not about apologising for being ill, but for the change of plans. I also wonder whether the OPs attitude here is a sign of her general attitude towards her son living with her.
It seems he got his shitty attitude from her, based on her updates.
Ps: I never want my adult children to feel like secondary citizens in their own home. Yes, the OP gets the final say in things because it's in her name etc, but when living together as adults, living as equals as much as possible seems the right approach to me.
And going down the 'i pay for most of it, my word is final' would be abusive in other contexts, ie cohabitation within a romantic relationship, so be feet wary of going down that route. it's not pretty and it's pretty low, especially if he can't afford to move out.