It seems like an odd comment on the behalf of the DM, but it's one that I'm not too unfamiliar with myself.
I have one male player who, at least in the past, use to play quite a number of female characters. Furthermore, most of these characters were exceptionally attractive and homosexual to boot. Worse still, when he'd write up a character background for these characters, they'd typically read like a bad porn script.
Now, at the time, my friends were running a lot of World of Darkness games and I, in particular, ran Werewolf. So, after seeing all these characters of his and hearing him talk about how he was still deciding on whether or not his werewolf in my game was lesbian or not, I decided to go into how the breeding urge is particularly strong in werewolves due to their small numbers and that, furthermore, homosexuality is quite strongly, almost violently, untolerated in their society due to that feeling among their people that they need to breed, breed, breed new warriors.
Normally I wouldn't do something like that. But this player just played some of the worst stereotypes that you can expect out of a male player with a female character. Had it been one or two, well, hey, no big deal. I don't have an issue with sexual issues at my gaming table and generally my friends don't, either, but if a characters inspiration comes from a porno, well, its place isn't at my gaming table.
He still plays a good chunk of female characters, but these days he generally just eliminates sexuality as a factor from them.
Now, perhaps the DM in question here had a similar issue, or perhaps he's homophobic. Can't say without more info on what was going on. For my part, I could see myself plunking some strange detail like that into the world; I like odd little cultural bits and don't particularly restrict myself on the topic they might take (for example, I see dwarves as being pretty much heterosexual nearly without exception but, by that same token, elves as being fairly bisexual; I don't think I'm the only one who generally stereotypes them as such). Certainly I add things like that to religions in my games - among the right people, those more controversial details help, I think, to better establish why a character (or player) might like or dislike a certain group, beyond just "Oh, they're evil," or, "Grrr, lawful!"
However, I certainly wouldn't do something like that if I felt a player might be uncomfortable or walk out on me.
I am curious as to this particular DM and players reasoning for what they did, though.