Great catch!
The Swiss controller argued they were only cleared down to FL280 - not FL250. Couldn't spot the original clearance. But at 0:57 into the first recording, you can clearly hear German Wings: "2529er decending FL 2-5-0". There is no objection from the controller at this point - she just asks about their current heading and continues. 2min later there's the TCAS RA...
At first glance, controller doesn't look too great here. But will be interesting to hear from the investigation. Hurray for TCAS...