Looks like there was a weak spot near the head which propagated to the neck. When I blow the picture up it looks like there is a dark region near the head which would be the site of the original failure. Since the case head is the thickest part, the failure went away from it going via the path of least resistance. That is in the direction of the case neck.
I've had this happen before in non-nickeled brass with the failure point being in the center of the brass. In one case the site was obvious since the split had an unusual feature which was the obvious failure location.
Looks like a case
of a bad draw
forming the brass.