He knows a lot about his domain, sure, but he's no god and there are a lot of areas he knows diddley-squat about.... user interface design for one!
And Einstein knew nothing about biology.
I'm sure he knows "diddley-squat" about most areas, but as long as he knows a lot about his domain then he's an expert.
And he is good at user interface design, and git is a good example of that; it's just not aimed at beginners. It was designed by and for expert users, and the interface fits that very well.
admittedly "expert" UIs are different from "noob" UIs, but the number of "git magic spell" followers out there mean that it isn't a good UI for the majority of people who use git.
Git being operable with a pry bar and repairable with a hammer is a good proof that in this context it's a good design.
You forgot "brilliant".