Hm. Sounds like she wanted to make you aware that she had a girlfriend so you wouldn't hit on her. Maybe she had bad experiences in the past, who knows? Technically she answered your question, though.

[ Prompto kind of looks like innocence itself, so he's fairly sure she didn't see him as a predator. Then again, Molly was not the best person at socializing. That's why he defaulted to just blind people with Mollymauk. ]

It's all very situational, too. Maybe she just didn't want to talk, just like any guy might not want to talk right then. Doesn't have much to do with gender but with everything else.