theres an element of you make your own luck in these things, normally a fall in cyclocross you dont break an ankle, and the conditions were a total one off, I mean for half a second he almost saved it by getting a foot down in time, but yeah it was noticeable that MvdP didnt follow others as closely, so gave himself the room, whilst Wout was essentially a passenger by trying to use maximum slipstream from MvdP and the thing with ice is youll be down on the deck before your brain can even process whats happening. and if MvdP had gone done in that corner, Wout would have crashed straight into him, thats kind of how risky that positioning was at that corner.
so yep bad luck completely, but was the reward greater than the risk at that stage ? there are totally ways he could have ridden it differently and stayed upright, but that might have cost his chance to win.