Like anything, I guess it's all how the individual feels about it. I would lean towards agreeing with your friend. I go back and forth with myself whether I am heterosexual who likes fantasizing about being with women to being bisexual but still preferring men. I've been with 2 women where we gave each other oral sex. I enjoyed it, but I don't think it changed anything about how I feel about men and women - I still prefer men. I look at it as an "exploring my sexuality" thing. I don't think it changes who I am, but it might bother someone I am with. On the other hand, if I had a boyfriend tell me he did the exact same thing with a guy, I would be bothered by it a bit. Hypocritical, yes. Simply because in my experience, straight men just don't think that way about other men. So if they do, then maybe they really aren't into women. I know that is just perpetuing the stigma, but that's just been my experience. It's more acceptable for a straight woman to be with another woman than a straight man with another man. Wrong or right that's my perception.
But I would be more open-minded to what he had to tell me about it because of my own experiences.