Look closely at the picture of the test chamber in the article. Do you see Helmholtz coils surrounding the entire apparatus? Nope.
https://en.wikipedia.org/wiki/Helmholtz_coil
It's the same story as the EMdrive: they run something at high current, without cancelling earth's magnetic field.
high current + earth magnetic field = force. This method is used to move satellites:
Not canceling earth's magnetic field (an easy thing to do) when measuring microNewtons at high currents is just very poor experimental practice. Unprofessional. Amateur.
"Experimental Null Test of a Mach Effect Thruster." https://arxiv.org/pdf/1301.6178.pdf
"The motion of the beam is damped by a pair of aluminum plates attached to the beam that move in the magnetic field of an array of small neodymium-boron magnets. The power circuit was extensively shielded to insure that stray fields did not compromise the results."
https://en.wikipedia.org/wiki/Lorentz_force#Force_on_a_curre...
"When a wire carrying an electric current is placed in a magnetic field, each of the moving charges, which comprise the current, experiences the Lorentz force, and together they can create a macroscopic force on the wire (sometimes called the Laplace force)."
It's basic. I don't think of the relevant people as idiots.