Correct, that's his genetic makeup. A short look on his face tells me: this is a no-bull guy who did his homework.
here's his delt and arm when he was in his prime
one of the most ascetically beautiful delt and arm that i've ever seen
on a side note, i showed a pic of Zane to a female friend of mine today and said to her "this is how i want to look like", and she said to me "no it's too big, i don't like it"