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Being a man that's attracted to men makes you gay. A man being attracted to feminine traits alone isn't gay, even if they're exhibited in a man or something else (like that squash everyone wanted to fuck). Certain signals will turn someone on as long as they line up closely enough, which is why traps and initially-convincing trannies can operate the way they do on any level.
However, a man who pursues engaging in sexual searching/activities with someone feminine even AFTER learning that person is also a man is knowingly engaging in homosexual behavior. That's when the downhill slide into heterosexual uncertainty begins, especially if it becomes habitual and you start rewiring your brain to start having gay-adjacent fetishes. If your "friend" honestly didn't know the person in the pic was a guy, then he can accept the new info and look for the traits that turned him on here in a woman, instead of this guy. If he still goes for it, then he's probably not a 0 on the Kinsey Scale. Though it's current year and no one gives a shit anymore.