Well, regardless of his flight hours, it wasn’t incompetence apparently. I doubt it was a health issue also as he was young (28) and you’d expect to hear something (gasping, moaning, etc).
We may never know this guy’s problem. Obviously, deranged and suicidal. Maybe he wanted his 15 minutes of fame? Every now and then someone just goes batsh!t crazy....it happens.
There is zero question that this was deliberate, as opposed to health-related. Airliners are not hand-flown at cruising altitude. This aircraft would have certainly been under the control of the autopilot/FMS at this point, and had the copilot been rendered unconscious for some reason it merely would have flown on in level flight until it ran out of fuel.