There is one part of this question that is not clear, and it could make a difference in your final answer. The question does not specify whether it is asking about McCandless's high school graduation or college graduation. The answer isn't much different between the two graduations, but I want to make it clear that McCandless started to become much more distant and solitary in college than he was in high school.
Prior to graduation (especially high school graduation), McCandless appeared to be a "normal," run-of-the-mill, well adjusted student. He got all As in high school with the exception of an F in physics. The F came because McCandless refused to format his work the way that the instructor demanded. Knowing McCandless, this isn't too surprising. An elementary school teacher pointed out years before that McCandless did things his own way.
Chris marches to a different drummer.
McCandless even participated in sports, and by all accounts, he was a fierce competitor. He was even team captain of the cross country team and "relished the role." Kids don't get elected or chosen to be team captain if they are only focused on their own glory. Team captains are team leaders. They care about the good of the whole, and McCandless loved helping his teammates improve both physically and emotionally. Runs were a spiritual thing for him, and he conveyed that message to his peers.
Krakauer does a great job of incorporating multiple testimonies from various classmates, and it all gives readers the message that McCandless's life before graduation was mostly typical. The one divergence was that McCandless preferred trying to help the homeless to partying with peers.
On weekends, when his high school pals were attending "keg-gers" and trying to sneak into Georgetown bars, McCandless would wander the seedier quarters of Washington, chatting with prostitutes and homeless people, buying them meals, earnestly suggesting ways they might improve their lives.