It happened when the box to a big drop to a hard surface on the end that would allow the counterweight to bend the arm that way.
Since the vintage gear was new, the distance traveled by an errant package slipping off a belt has risen by a significant amount. Drops of over 20 feet are probably within the realm of possibilities and I doubt any tonearm with the weight attached (most P4 mounts mostly) will suffer when this happens. It shouldn't. Good luck with the claim.
I agree this is what probably happened...
When shipping TT's, ALWAYS remove the weight and the headshell and pack them seperate in the box.
Was it a Technics SL-Q200? I had that table and the arm was identical.

OK.. didn't know that.
In that case, it's best to support those parts with foam or styrofoam under and around them, and tape down very well.
