It seems all young actors, in Hollywood especially, try to get the buzz out there that they are packing. It is amazing how that sort of thought can make everyone want to "find out" one way or another. It also gives a lot of attention to anyone who claims to know for sure. "Yeah, I saw it. It is epic! I'm telling ya, that thing is huge." When and where that viewing could possibly have happened is harder to pin down.
On the other hand truly hung actors actually seek out photographers who want to do "artistic" nudes. Even if the shots never see the light of day after the photo session, between the photog. his/her assistants, make-up and so on, enough people have actually seen the real "pant serpent" that the word is out in no time. His penis quickly becomes a celebrity in its own right.