This book can be summarized in a series of personal ads:

Suburban DC boy seeks understanding from mysterious land. Not into sharing. Reply next week.

DC Boy: Lonely American Cowboy Desert calling. Etch your name in my skin.

Freaky Cowboy Desert: DC *Man* says thanks.

DC Man seeks virgin expanse. Must be big and wild.

DC Man: Denali here. Will take it all. Are you *big* enough?

Indulgent author seeks Reason for DC Boy's death. Will kiss and tell.

Basically the same story as LostInWoods, as we just need to s/family/cocky boy/g. According to Krakauer, he dies of local flora toxicity ignorance. According to me, self-poisoning looks like the proximate cause. The root cause seems like failure to understand what the Denali National Forest looks like during the summer. Spring thaw floods last throughout the summer, all low terrain becomes water-saturated, and even in summer the DNF lacks the relative superabundance of sugar, protein, and fat that exists in the south.

The boy just hiked in before the spring thaw, got trapped behind the thaw floods. Lacking a good map, he couldn't find his way out. Lacking a secure source of food (didn't know how to cure meat quickly), he found himself on a subsistence diet. Exhausting all local known edible flora, he ate a plant which supposedly contained swainsonine, which binds to all the amino acids and glucose that it encounters, preventing their metabolization by humans at least. Drink lots of water and eat a lot of protein and sugars to remedy the poisoning. Stored body fat and protein can be used by the body to flush the poison. Lacking those stores, a subsistence human will have a marginal chance of surviving unless they acquire large amounts of protein and sugar.

He died alone in the woods. Even worse, his mom woke up in the middle of the night:

"I don't know how I'll ever get over it. I wasn't dreaming. I didn't imagine it. I heard his voice! He was begging, 'Mom! Help me!' But I couldn't help him because I didn't know where he was. And that was all he said: 'Mom! Help me!'"