I can tell you, at one time Palumbo was a walking FREAK of size and mass. I sat with him at a meeting in the late '90s and was awestruck with his sheer bulk. He weighed around 315 and was VERY lean.
When an individual responds favourably to anabolic drugs and hormones and is willing to use LOTS, and is consistent with his weight training and eating (the latter, relatively speaking), the growth potential is amazing.
Becoming gigantic = access to and a willingness to use (lots of ) anabolic agents + good genetic response to said drugs + consistency with working out + considerable food intake.