I have received several other batches of eggs through the mail this winter, and I think most were marked "eggs" and "fragile". Two eggs were broken in one other box, but there was no external damage on that box and for the most part the other boxes have arrived in good shape.
I dunno what happened to this one, but it was impressive!
My local postal workers felt horrible about it. Today when I called about another box, they remembered who I was and asked about how the eggs were doing (the squashed box arrived last week). So I certainly don't blame them for it. Just bad luck somewhere along the way!