Of course his mum was mad. Fuming mad.
This guy has exiled himself voluntarily. He lives in his room, emerging only for the necessities — but only when nobody else is around.
His habits are frowned upon by his family, but their hands are tied. It’s a lifestyle choice he wants for himself and it works perfectly fine for him.
He enjoys the independence, he glorifies the lifestyle, he is self-sufficient. There is nothing he can’t do. But one night while sneaking out to replenish his water supplies, he gets into a confrontation with his mom.
It’s not fair to be treated like a hotel, checking in and checking out of family life as he pleases.
He snaps. They both snap.
He checked out of family life long ago, but the family hasn’t left him.