I mean, for some people, it is. When you’re exploring your identity, you don’t always get it right on your first try. Just like there are people who are convinced they’re straight that are actually gay (or bi, or pan, or what have you). Though that is far more common, largely because of the societal pressures to conform to heteronormativity.
But then, perhaps that truly is Vance’s case here. Maybe he actually is gay, and his whole… everything is just him trying desperately to convince himself otherwise.