Earlier quoted context omitted.
I think he meant that evidence of your drinking might still show up on Facebook, especially if those photos are tagged with your name.
I may be wrong, but unless your aunt was then browsing your friends posts / was following those friends, she wouldn't see those photos.
Mine are set in such a way that you can't add me as a friend if you're not already friends with a friend of mine. If we then are friends, you can't post anything to my wall nor can you tag me in any way without my consent. Granted, the picture will still be there (and possibly visible by anyone if it was posted by one such clueless individual), but then again deleting your Facebook account won't magically erase all the pictures you appear in either.
The actual problem is that any idiot has a smartphone and a Facebook or Instagram account. And they take pictures. And post them.
There doesn't need to be any aunt following your friends. A cousin is more than enough. And there are countries where related families tend to be scattered over a relatively small area, so having friends in common between you and your relatives is but a rare occurrence.