Straight guys flirting with gay guys

Ive had a straight guy before flirt with me, I thought he was into me until I saw his Facebook profile, then I was very disappointed that said he was in a relationship with a girl ...... anyway he still flirted with me .... it was very confusing. I also had a ex best friend flirt with me, and when I confronted him about it he proclaimed he was straight. An example of this memorable time he flirted with me: we were sitting on the couch together watching a movie and he says out of the blue 'hey blake, why don't you get on the floor and ssss----securely fasten my shoe' ...... frakin hot right?! As far as i know neither of them knew i was gay as they were flirting with me. Anyway my questions for you guys are: 1) Why do you think guys flirt with other guys like this? 2) Do you have any experiences to share?