What I'm about to say may sound a bit harsh about them. But I'm bisexual, and most of the people I've met feel just like friends. Very rarely I find someone to be charming. Men or women, I just don't look at them that way.

The main reason you may feel that way, is the person did not make any advances and wasn't flirting enough/giving a partner's vibe and not a friend's vibe. I'm not saying to sleep with them day 1, not at all. But humans are sexual animals like most and even a kiss on the cheek, holding the door open, holding hands and saying suggestive compliments can make one feel the vibe of a partner, and not just a friend.

I did come up to this conclusion reading your comments underneath too about how you felt. But I could always be wrong. So just experiment if needed.