As Pecker said, the guy's scrotum is probably saline-filled. His balls would not have enlarged from this process... basically the procedure is like filling a balloon with water.
If it's larger nuts you want, I do know that some people buy vacuum tubes designed to pump testicles. I do not know whether this technique produces lasting results or if, after any number of pumping sessions, the testicles become damaged. Seems to me that permanent damage could occur, as an ex of mine had been hit in the groin repeatedly with a basketball (wielded by a mean-spirited teenager) and as such lost his ability to cop a nut without ivolving tremendous effort. (Sex with him really sucked, and he always had to whack off in order to cum).
Of course, you could try slamming your nuts against a hard surface until you pass out from the pain and see if edema occurs. But I think the answer here (as I am neither a fan of vacuum pumping nor testicular pain) is to be happy with what the good lord gave you. As BigPaul said, it's not the size of your nuts that makes a difference in sperm production. Diet and vitamins can perhaps help you achieve that goal. I have met guys whose balls were the size of Cornish Game Hen eggs who could shoot quite admirable loads, and guys with grade AA egg sized nuts who dribble.