Skier should have checked up when he saw a lip coming up. Roll overs that big are pretty obvious before you get to them and you shouldn't drop stuff that you've never skied around or have a spotter. That said... it does come out of no where. That was a pretty open space between the trees and not like he went too far off the beaten track. Probably should have been marked as a cliff by patrol.
Nothing wrong with following tracks. But you need to ski cautiously and always try to have an obviously bail out option or at least know the terrain enough to know where the tracks will put you.