Wow. This is about your ability to be charitable, not the standards you wish you could hold all others to. And yes, in a religious context, where (in more than theory,) you are supposed to take the religious lessons seriously.
It’s not just about whether or not he is mentally ill- and yes, he may simply be stressed beyond what a sheltered young person can imagine.
My kids and I did long term meal site vol work- very different than serving to the congregation. We heard all sorts of stories. And our guideline (that of the group, expected of every member) was to feed the people who came and show them dignity. If it ran out and some came in late, someone would find something, even PB&J.
Think about it. The Quakers have a nice expression: putting faith into practice. Goes with “practice what you preach” or what is preached to you. Think about this experience.