It looks like an impact because it is broken all the way around the hub, not just cracked in one spot, but then the fork looks relatively straight. Maybe once it cracks on one "spoke" the others don't have enough strength to hold up the weight of the bike/rider and that's when they all failed. All of the "spokes" failing at one time seems to unlikely says I.

Wes, I can actually make your show next week! Yay. Finally. I can't make it friday though, due to being in Montreal.