A failure like this can only come from 1) bad design, 2) bad alignment or load on the bearing, 3) bad installation or 4) parts problem. 1) can be ruled out since this is a first for this failure, that leaves a choice of those other three. That shaft  is suspended by those two bearings, the front one is fixated axially, the rear is not - which makes sense as the aluminium of the engine will grow more than the shaft. But does the rear bearing run into a stop somewhere? And is there a way to check the shaft alignment? I would also be interested to know where the debris of the bearing went. The damage while bad now could have been worse. Hope for the owner that that head is recoverable. Nice pictures of the innards by the way, that crank looks the part.