the most stupid question i got asked today

i got a new colleague, (24 years old) we got along quite well from the start and during break i was checking my phone and she got a sneaky peak at my homescreen, a picture of me and my bf. Immediatly she asked - who is this? "My Boyfriend" i answered and she started asking more questions, things like - how long have you been together?, are you living with each other? the usual stuff. I didn't mind as she was really friendly and cheery during the conversation, then she asked: "Do you guys have a lot in common?" i smiled and told her that we are actually quite different and she interupted me right there asking: "Is he gay aswell?" .. what? how is this a legit question after the previous conversation?