Nearly all the guys in gay porn have a feminized ratio i.e. their index and ring fingers are the same length from what i've seen. Especially twinks.
I seriously doubt there is any clear correlation between performing in porn and index/ring finger ratios. My guess is you're looking at a pretty small sample that just happens to fit that pattern.
Just from observing mens hands myself I never see a guy with equal length index and ring fingers who is straight. The only guys I've seen with it are gay.