What a couple of chowder heads these guys are...
They made a study of 63 papers previously published to get their results. That is, they used a set of statistics to get a "new" statistical result. This appears to be a case of Data dredging making it a fallacy of statistics.
We have no way of knowing if the previous studies all used the same or very similar methods to reach their results as but one example of the problem using the method these two psychiatrists did. We don't know how many papers have been written on this subject either or if the data was cherry picked for their study.
Bottom line, they proved nothing but the obvious fact they aren't very good with statistics.
I don't know if their hypothesis is correct or not, but they didn't prove anything using their study towards it.
You could be right but of course you can't be sure until you check those assumptions. You haven't disproven them but have made a good case for doubt about the thoroughness of their research. I will personally side with this articles conclusion because it very much echoes my personal observations on this matter.