Just look at the arm that you flex all the time when someone says make a muscle. It is usaully a lot better than the other one.
I always flex my right arm when asked to "show me your muscles" even as a little kid. But that's because that was my bigger arm in the first place and that I am right handed. BTW, I always did some extra sets for my left arm to "even them out" and it made zero difference. I still do. When doing unilateral work my first set is with my left and my last set is with my left. It's just out of habit. Now that I think about it, I think I should stop. I mean, if it hasn't made a difference after 40 years of training it's not going to make a difference now.
It's like when someone was saying that doing construction work makes you stronger and gives you bigger forearms when in fact a weak person is far less likely to take a profession that requires physical strength than a strong person.
Arnold's right bicep always had a better peak than his left. Even as a teen.