I agree, if he doesn't want to tell you leave him alone. As much as people are going to hate me for this you are not entitled to knowing or being told about someone's gender identity if they don't want to tell you and prying or demanding to know otherwise or worse semantically trying to determine it using "signs" is incredibly disrespectful.
Reminds me of my friends a few years back, the difference is that I was having a conversation about having a boyfriend who's bi or pan since it might be a turn off that I look too much like a girl. Boy did I sure get grilled by them for that one.
I do wo der if a hetero/gay partner would consider "becoming" bi or pan just based on them liking one how one is. Like, if ya came out to yer boy/girl/enby-friend, if they'd consider just being fine with it.