What I understood from the article: it's not the engine that rotates.
Instead, the fuel mixture ignites in one spot, and the explosion spreads at Mach 5 around the engine but once it reaches the end of the combustible fuel, more is injected behind it so the explosion can just keep traveling around in circles.
Judging by the article they managed to get that working, and also came up with a better way to take videos of this happening (high speed camera, tracer chemicals in the hydrogen, better signal strength).
That was very different: conventional rockets for ground-to-orbit, but landing with folding helicopter-like rotors. I think the original concept was to use the helicopter rotors to get to high altitude before throttling up, which was supposed to save a lot of fuel, but that was dropped pretty early.
Here is a video from the Technical University of Berlin where the transition from ignition to the continuous circular detonation was also filmed among other things.
Instead, the fuel mixture ignites in one spot, and the explosion spreads at Mach 5 around the engine but once it reaches the end of the combustible fuel, more is injected behind it so the explosion can just keep traveling around in circles.
Judging by the article they managed to get that working, and also came up with a better way to take videos of this happening (high speed camera, tracer chemicals in the hydrogen, better signal strength).