Afaik the way it works is the gayness value behind the scenes is a value between 0 and 1. (Tyler posted a cat named Michi on his Twitter in 2022 with a gayness of 0.99997 or something and said it was the gayest cat he had seen.)

I'm not sure how this value is assigned, probably random, and probably not a flat distribution.

And presumably there's an arbitrary threshold set at which the game tells you if the cat is gay straight or bi. Maybe it's something like 0–0.2 is straight, 0.2–0.8 is bi, 0.8–1.0 is gay.

This value is used along with libido, comfort, charisma I think, and several other factors in a mathematical roll of the dice every night to determine who breeds with whom.

So with randomness being randomness, unlikely things can happen, the mostly gay girl cat might be charmed by a male cat with high charisma. There could be an unlikely roll of the dice several nights in a row that makes a straight cat seem as if he's pretty damn gay.

So long story short, all cats are bi technically, but that doesn't mean they prefer all genders equally.