The problem is that this happens within normal spec. He explains it in the video.

So you’re probably fine towing at the rated limit… as long as you stay on flat ground. As soon as you crest a hill, all that weight becomes vertical for a few seconds.

Additionally, aluminum stresses over time, like bending a piece of plastic. The first time you do it, it might be fine. The tenth time it might not.

The Cybertruck is not for serious towing.