I'm not sure that I agree with you on this Slim. I have been with my share of young ostensibly straight guys, looking to be sucked, or jerked off. I often see the same actions by these guys, who are not posing for a video camera. I've found that there does appear to be an innate set of actions that a young man goes through while being pleasured. These actions often include the hard breathing, massaging their own chest or sometimes their tummy, throwing their arm's behind their head, or in this case, putting an arm over the sofa.
I've often been amused, as well as aroused, watching young guys go through the exact same motions while having their dick sucked or stroked. I believe it is a natural part of a young guy's sexual make up. It's sort of like watching a nature film, and seeing how all male member's of a certain species mate and reproduce using the exact same actions and gestures. It once again shows how man is a mammal, part of the animal kingdom too.
But you may be correct, that part of it is trying to look like a "porn boy", but I do believe that a larger part of it is "just doing what comes naturally".