it's just saying that just because he's a world champion means they get the best testing, I think that may not be true. Plus he is (currently) junior world champ so that won't be as harsh on forks as the elite routes (I do know he is capable of the elite routes before you say).
To be World champ you have to have some pretty dialled techniques and ride in an efficient way. I think that wouldn't be as much of a test as someone who doesn't have as good technique and relies on forcing the bike around with brute force. As Dave said too, falling off can be pretty brutal on forks, I bet there are riders out there that fall off more than Jack does.
Don't get me wrong, I think these forks are pretty good, if you run a front magura forks generally don't last long and if you don't want the weight of Trialtechs then the Karbons are a good (if pricy) option.