You're getting them, aren't you?

I was about to say 'til someone else beat me to the point: hardons can become as contagious as yawning. If the sight of his manhood in turn prompted a reaction of yours, it's normal. And, dare I throw it in, entertaining the thought of sexual behaviors even isn't enough to deviate from heterosexuality. Perhaps -- and there's no light way to put this -- if you developed some feelings toward not just that one particular man, but men in general, then you would have your doubt. Otherwise, man, don't worry 'bout a damn thing.