The Chinese tests did not include testing in a VACUUM. Not a sealed chamber, but an actual, airless, gasless, box of some sort.
The power levels involved in these devices are 10-20 kW - that much power into anything is capable of heating air and producing currents from convection alone. A microwave cavity is exactly the sort of thing which would make a great make-shift reaction chamber for a very inefficient, very ordinary jet engine of some sort.
I note the Wired article here also makes no mention of whether they tested the device in a vacuum chamber. Its the only test which matters, and no one ever does it, meanwhile they're pumping enough wattage to flash boil water around things.
EDIT: From the NASA abstract as well - "Testing was performed on a low-thrust torsion pendulum that is capable of detecting force at a single-digit micronewton level, within a stainless steel vacuum chamber with the door closed but at ambient atmospheric pressure."
Given what this thing claims to do, and how you have to operate it (allegedly) and the scale of the forces involved (tiny), not testing in an actual, evacuated vacuum chamber is absurd.