Reading the study doesn’t inspire a lot of confidence in their methods. They make a lot of basic errors like listing dB figures (a relative term) when I think they mean dBmw (an absolute measurement).
They tested multiple frequencies but for some reason only 2450MHz showed significant effects. 900MHz and 1800MHz showed no effects, despite 1800MHz being relatively close to 2450MHz.
They also didn’t use very many rats for each group. Only n=6 per frequency, which were further divided into n=3 for some of their measurements because they couldn’t use the same rat for both tests. They also chose a lot of stress-related measures which are known to be heavily influenced by mishandling the rats (e.g. if a researcher accidentally dropped one during handling)
Unless someone can replicate these results and do it with more rats, I suspect the results are likely from one or maybe two rats having abnormal baseline results and that being amplified by the ultra-small sample size.
As for relevance: Unless you’re standing in close proximity to a high-gain, directional antenna emitting continuous wave tones (not intermittent modulated WiFi packets) then your WiFi exposure won’t come anywhere near what they used for these experiments. Inverse square law and omnidirectional antennas mean that very little WiFi energy even makes it to people near a WiFi router.