I think they’re using that as a theory because there are (fairly rare) cases of people “catching” auto immune diseases from transplants, so that may be the mechanism behind what happened to this guy.
However, alcoholism isn’t an auto immune disorder, so far as we know.
Turns out psych drugs also act on other things besides neurotransmitters, so it’s not surprising if stem cells have multiple methods of action. Considering what they are, it would be weird if they didn’t.