They are right, he is not above the law and has to be isolated if positive. I don't think Samui has a home isolation program that would be able to accommodate him. Obviously shouldn't have taken his passport though but yes, if you don't pay your hospital bill, you can expect to be deported in many countries or have your visa cancelled or not able to renew. Wonder what he is "volunteering" for now after his restaurant went out of business. If it's like all the other volunteers that suddenly popped up after the borders closed, then he shouldn't be bringing attention to himself if he wants to stay in Thailand.