He is actually very broad, right? In this panel his pectorals are defined, and his shoulders are pretty rounded. His arms look thinner compared to his torso. He is muscular and lean...you can see that his stomach is flat, but there isn’t much definition, and his waist is small.
In the anime they've added definition. His abdominal muscles have more depth, and the obliques and serratus suddenly appear... the shading makes his stomach almost concave looking.







