Depends on the person. Some people are more in the middle, some lean one way or the other, and others are more fluid and their attractions shift. There’s a whole spectrum of bisexuality. It’s also why there’s a distinction for pansexual, for people whom gender plays no role in attraction at all.
Sounds like your friend might be bisexual heteroromantic. Happy to sex up anyone, but only romantically attracted to the opposite gender. I’ve had a few friends in similar boats of differing sexual and romantic attractions.