That frame was most likely packed in a box without dropout-savers and adequate padding. The dropout-savers keep the spacing between the dropouts constant in case the box is impacted from the side. There is also typically a cardboard box underneath the rear-dropouts and under the BB-shell. In this case, it appears the dropout was resting against the bottom of the box. Then that box was tossed off the truck as typically the practice. Upon landing, the weight of the frame+box+padding was loaded on the bottom part of the derailleur-hanger and bent up the dropout slot.

The repair is not a problem if alignment is verified. All of the rider's weight goes upward into the top part of the dropout. The only thing the bottom half of the dropout holds is the rear-derailleur and part of the rear wheel's weight when getting air.