Stress relief is indeed healthy, but punching things when you are angry or sad is a form of violence that can and does easily turn to abuse. By the way, I friggen' love hiking and anything related to it. It clears your head more than anything in the world.
As far as the kid's sincerity is concerned, whether or not he may kill himself... you're right. It COULD be a desperate plea for attention, he may very well be fine. But shit man, I'm not going to gamble on a friends life for any reason. Even if it is a ploy, he is obviously desperate and needs help dealing with his depression.