No surprise. This has happened to pretty much every commercial jet out there. I flew the Classic 747 as a freighter for 16 years and everyone knew to load the forward belly first and offload it last. Of course, we were careful to get pallets into A, B, and C comps up top before anything else and offload them last.
This incident had it’s start with the “charter” department at United. While they were arranging the trip support they should have asked very carefully about how many 737-types the ground service company works. “Few” to “none” should have triggered a need to send along or preposition a ground rep. No one uses a tail stand for pretty much anything around the United “system” because they know not to unload the front first. Also, the crew should have offloaded the pax a bit more evenly out of caution, but they likely weren’t briefed either.