That doesn't make any sense.
He literally does look like that because he cycled steroids his entire adult life. He's a textbook case of what you can do with steroid. He took the steroids to get big. He didn't say to himself, hmm I'm already huge and a genetic freak, but I'll take steroids just because I like wasting money.
I'd argue his genetics, being the science experiment that he is, are probably the least consequential determinant of his size out of this list:
1. Mentality/focus and stress.
2. Calories consumed.
3. Training volume in the gym.
4. Magic get big formula.
5. Rest.
6. Genetics.
Yeah I'll take that list, in that order as order of importance. And I'd say 1-5 probably makes up 99% of it. Basically all his genetics did was give him height and get out of the way of his elixir.
EDIT***
And yes I have done multiple cycles of steroids so there is my personal bias/experience fwiw.