Your friend may "live a so-called straight life, but the way he grabbed your dick and stroked like that is a man that's done it a few times before. 50 Shades of Bisexuality..
a friend of mine in high school reached over and grabbed my cock at the urinals in the gym, neither one of us could believe how fast I got rock hard. He called me homo in private after that cause I got a boner. He pretended he was just kidding around, but I didn't believe that.