how is this initial description fitting when we find out more about each man?

Steinbeck always  begins his characterization in simple terms. 

George is described as physically small with very sharp features while Lenny is described as almost the opposite,

"a huge man, shapeless of face, with large, pale eyes, and wide, sloping shoulders; and he walked heavily, dragging his feet a little, the way a bear drags his paws."

Both men personify their original dscriptions. Steinbeck fills their characteristics in as the novel progresses.