This incident occurs in the very first chapter of this excellent book, as Gallien gives Chris a ride in his car to where Chris leaves him to walk off into the wilds of Alaska by himself. Gallien never knew this at the time, but he was the last person to see Chris McCandless alive before his self-imposed isolation and then death in the Alaskan wilderness. However, when Gallien and Chris talk during the ride that he gives him, it is clear that Gallien does not think that Chris is some naive youngster who has no idea of how to survive by himself. Note what we are told about their conversation:
It was a two-hour drive from Fairbanks to the edge of Denali Park. The more they talked, the less Alex struck Gallien as a nutcase. He was congenial and seemed well educated. He peppered Gallien with thoughtful questions about the kind of small game that live in teh country, the kinds of berries he could eat--"that kind of thing."
The importance of this quote then helps to set up the dilemma that dominates this book. Chris McCandless, in so many ways, appears to be just another wacko wanting to live out his Jack London fantasies. Yet at the same time, such intelligence and knowledge about local berries and wildlife means that we can't just dismiss him as such, which leads to the quest of the novel to try and work out why he did what he did.