It's a Dad Joke community, it should be oriented toward corny jokes and groan-worthy puns, that only a Dad would love. Don't tell "Dirty Jokes" here. We know what they are. (didn't someone make an "uncle jokes" community for those?)
Having said that, simply noticing that gay and bi people exist (and can also tell dad jokes) in no way qualifies as a "dirty joke". I mean, we talk with kids about people with boyfriends and girlfriends all the time, and tell corny jokes about them, without getting all ooky. Pointing out a couple with two boyfriends isnt any different.
I saw that joke and it made me chuckle, if I were mod here I would have left it alone.