So all this happened at an airfield in Germany?
If it is a full-size, remotely piloted version where are the certification papers and NOTAMs required for legally flying an untethered SUAV of that size? Germany has rules about that sort of thing.
Personally I'm still sceptical and will remain so until the videos stop using the typical tricks used to obfuscate the size - showing it with nothing at all in the frame to scale it being one of the main ones.
I also don't believe that fans which are lifting what must be over 1,000kg of airframe could be anything like that quiet.
PDR