Folks here are saying it's a prosthetic. I don't know, personally. Seems like a scene where they could just as easily done implied nudity, with his left leg forward a bit to hide his penis-pouch. I may be wrong, but I thought prosthetics were more common when either the character was made out to have a big dick (like
Boogie Nights) or where something traumatic and/or comedic happened to the dick, like Will Poulter's in
We're the Millers. But I may well be overthinking that. I checked on MrMan.com, where they usually tag videos and images with "prosthetic" when a fake penis is used, and they did not with this one. But that could simply be that they weren't sure.