I think at best its bi. I very bi, and our friend is what I would consider straight. He's 55yo, and up until meeting my wife and myself, had never had any sexual contact with another male, and apart from me, doubt he would again. But he loves me sucking his cock in front of my wife, he'll also have me finger his ass at the same time to add to the pleasure for him, but even when I do all this, I still feel its more of a power exchange than anything, although i'm very bi, i've never sensed he has an attraction of any type to males including myself.
He does it to show all in the room, who is the sexually dominant one. We partake in me rimming him reasonably often, so yes he is being anally stimulated, penetrated by another male, but he still holds the power in that act of dominance and submission. It could be a gay act, its definitely a bi act, but he likes solely for his own selfish sexual pleasure and power, not because he's attracted to men.