Before the internet, "cross-over" performers (either straight-to-gay or gay-to-straight more or less flew under the radar of most. Unless someone watches both gay porn and straight porn, there wasn't an easy way to notice. I imagine there have been millions (billions?) of scenes on VHS, DVD, Betamax (lol) with cross-over performers that have been lost forever. Men have done this since "moving pictures" were invented.
Labels like "gay" and "straight" and "homosexual" have only been around a couple hundred years.
Men have been fucking both men and women before there were even words for "men" or "women". Think about prisoners, soldiers, sailors, explorers, and other men who didn't see a woman for months, or years, or decades? Do you think they said, "I'm not gonna fuck that guy. I'm 100% straight. I like pussy." No. No one ever said that.
Gay men are a joke unto themselves. I'm mostly gay, homoflex, married to another "dude" for the past 20 years. I would never be in a romantic relationship with a woman. I've had sex with thousands of men. I've had sex with a dozen women. Does that make me a "fake gay" or even "bisexual"?