It's quite possible that the causality goes the other direction, and a baseline population of brain disorders is being ascribed to the last notable thing that happened to them (which has also happened to ~ the entire population at this point).
Not really, since the survey paper notes that the EEG pathologies were detected in 69-96% of patients, including children. It is not plausible to propose that 69-96% of patients, including children, had undetected brain disorders and that was the direction of causality.
If they’re only testing people with symptoms, the causality could easily go either way.