Kudos for the smooth question-answering! That's probably the best answer you could have given in that kind of situation.

My guess is either A) he's one of those creepy guys who thinks lesbians are lesbians just to get the menfolk all hot-n-bothered with girl-on-girl action and thus wants to find as many of them as he can and zeroes in on womenfolk who aren't currently engaging in social interactions with other people, or B) he's a creepy old guy like my grandpa, who doesn't realize that he's creepy and that if he had a functioning brain-mouth filter, he wouldn't be creepy.