It can be, if the man doesnot have any prejudgement and he just find it convenient or he was just drunk i dont see any problem with it.
I was practically raped b4 by a woman, she gave me alcoholic drinks till i was too wasted and she mixed something into them and took advantaje of it, i can remember everything cuz alcohol and drugs have a hard time taking down the phicological structures i've built in my mind to control my behavior and i rarely get to totally black out, still my inhibitions were shut down i got an erection and things happened.
I enjoyed it, had a lot of pleasure, does that makes me straight or bisexual? nope.
If a straight man decides to have sex with another man, can be out of curiosity or necesity cuz he might find it convenient, cuz he learned that guys can be an alternative and easy to get source of pleasure, and yeah, we are kinda amazing at giving pleasure to another man cuz we know every single trick there it is cuz we are men too, and also hooking up with a man is way easier, with no protocols or annoying stuff, we do not behave like prices to be won by certain actions (or at least most of the time)
what is suposed to decide if you are gay or straigh are your deep desires and wishes, also your heart, can you be sincere with yourself, ignore the rest of the world, their judgement and their labels and ask yourself, am i able to fall in love with a man?, do i desire a man? do i imagine a life, a future with a man? and you will get your answer. Now if you think deep inside being gay is wrong, or you feel socially presured to not be gay, or you are ashamed of it or you just are afraid, you can bet you will never get to answer that question honestly to yourself