As someone already mentioned, there are people in this world that do nothing but sit in a cubicle all day. They sit there, eating junk, and generally feeling miserable for 8+ hours a day, then they get in their car and sit in said car for 1+ hour(s) a day in traffic.
Then they go home and sit on the couch.
It sounds like he had more serious health problems than "sitting too long" to begin with. If you sit for so long, and you ignore the actual pains and warning signs from being so sedentary, then you're going to run into serious problems. If you start "fading out" when you stand up from your marathons, then you need to tackle that problem and go for a walk, or do some squats or something, because it will only cause a lot of problems that will give you discomfort. You'll get headaches frequently, you'll get fatigue all day, etc. Starting ignoring all that, then you have a serious problem.
Perhaps it just wasn't his day to begin with.
Sad to see this young man's death being exploited like this.