It would depend on knowing more about the uncle and the family, I think, because mentioning the specifics might turn into more than you wanted to deal with because of the nature of the topic - and I supposed it's possible he was so utterly off it he forgot who you were - but at minimum, LW, even if you really think this was just him being drunk and stupid, it's probably still a good idea to tell both him and the family that you don't trust him drunk and he shouldn't either because some of the things he does drunk that he deeply regrets later, and avoid him in any circumstances where there's alcohol.

(Usually people who don't completely change when drunk - but he does seem to have apologized without prompting, so he realizes he shouldn't have done it; even if he secretly thinks what he did is ok, he's using alcohol as an excuse, and you should still avoid him and alcohol at the same time.)