His anatomy deviates a fair amount from standard proportions and make him look lanky and a bit awkward (which is ok, some people do have that kind of a build), is this intentional? 

What contributes to the arm looking odd is that bicep and deltoid are puffed up as if flexing, while the rest is in relaxed position. Even in someone with very buffed up biceps and brachialis, those two can look surprizingly flat when relaxed.

Brachioradialis origin curves in abruptly again like it it flexing ratherthen relaxed, same with digitorum flexor group. Those two grups of muscles cant flex at tbe same time because they are antagonistic group. One is adductor, the other is abductor.

Those are few immediate things that jump out at me about the arm. Some could be because of extreme perspective used in the pic.

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