When they made that comment about Captain America's *** I immediately thought of Spiderman because there was a photo of Tom Holland on set And his butt that went viral lol, the poster could be a nod to that, but it's kind of weird in the films of course because Spiderman is still a teenager in highschool.
The Captain America line actually ruined a part later in the film though during a serious fight scene where he rolls over and the camera seemed to focus on that area a little too long, and I just remembered that quote from earlier lol. That's the problem with trying to balance the humour with serious parts I guess.