Is this product even possible, page-91

Exactly what I was looking for, thanks David, Key quotes

It has to be mentioned that due to the limitations regarding the maximum displacement of an electrostatic speaker caused by the so called snap-in
effect, the maximum sound pressure is limited by the underlying actuator principle. Using a piezoelectric device would greatly enhance
the maximum stroke level and therefore the achievable sound pressure

So I think that confirms it - it's got to be piezo, so the original electrostatic patent isn't relevant. I'm interested what the "micro-pump" is as it seems like it's delivering better performance than I can find in any comparable devices

The authors would like to thank Alexander Bergmann, head of the
Institute of Electrical Measurement and Sensor Systems at TU Graz,
for providing the micro-pump used in the experiments

I wonder if this is a R&D sample or something that's manufactured at scale?

Their method of measuring acoustic response is a bit funky, normally you'd measure levels at 1m in an open area, instead we have a closed tube with a microphone in it, so I'll concede that this research at least demonstrates the audiopixel earphone speaker solution is possible, though with the caveats of: What was the micro-pump? They link to this https://www.ipms.fraunhofer.de/en/research-development/mesoscopic-actuators-and-systems/microfluidics.html but the page doesn't work