It's the other way around, it's with the ringer finger longer than the index that the guys might be gay/ bi.
Basically it's prenatal testosterone and can happen at different stages of development. Babies can have masculine brains but have small balls and no athletic ability and small ring fingers, or have feminized brains, big dicks, normal atheletic ability, and small ring finger, depending on the stage of development where testosterone was lacking.
But overall, the babies with smaller ring fingers have less testosterone and will have problems related to less testosterone like smaller nuts, more prone to depression, anxiety, less muscle mass, less sexual partners, and possible homosexuality