there may also be political pressure, but mainly there is just a strong demand for more papers, which means getting results that are publishable. "fluoridation has no effect on IQ" would be less publishable. same as in the west, but the western bureaucrats are more realistic and more focused on quality so the pressure is not as strong.
What's surprising is that if there was fraud one would expect the results to go in the other direction since fluoridation is the official policy.