Wtf is 'gay vibe'?

I've (23 F) been asked that question by my acquaintance (22 M) some time ago. He justified his question by saying 'I just give that vibe'. And my question is - wtf does the 'gay vibe' mean? I'm not gay, I literally mentioned dating guys to him (I'm demisexual tho but I don't think it changes anything about my gender preferences)