The three adjectives "thin," "lonely," and "clever" aptly sum up the character of Cecil in "The Moose and the Sparrow." In combination, they also help to explain why this young man feels so hopelessly out of place at the lumber camp, surrounded as he is by men who have absolutely nothing in common with him. Roughneck macho types like Moose have nothing but contempt for what they regard as a "college boy," a weedy-looking young man whose superior intelligence they clearly regard as some kind of threat.
There's a clash of cultures going on here. Blue-collar guy Moose harbors an instinctive loathing for someone he perceives as his exact opposite. Whereas Moose is full of beef and brawn, Sparrow is thin; whereas he's a gregarious outgoing sort, Sparrow is shy, lonely and withdrawn; and whereas Sparrow is a highly intelligent young man, a law student, no less, it's highly unlikely that Moose has received any formal education.
However, in a classic case of the worm that turned, it appears that Cecil eventually gains his revenge on Moose for all the insults and humiliations he's heaped upon him. Though it's never explicitly spelled out, it's almost certain that Cecil kills Moose, although it appears to everyone that his death was a tragic accident.