But the trailer didn't get away scot free....

Notice that the hitch arm was bent as well as the seat stay on the bike. The white mark in the upper picture is where the spokes were repeatedly bashing the hitch arm. The break occured where two holes were drilled through the hitch arm. Why were these holes there? I have no idea. But they did make a weak spot that bent/broke in the crash. Perhaps it was a crumple zone by design?