This study is really just confirming common sense, so I think you're being too harsh here. Obviously sometimes a person can legitimately have had a bad boss previously, but a lot of the time if someone is badmouthing their old boss/roomate/girlfriend it suggests a good chance of them having issues.

If you think your job depends on qualified interviewer anyway, good luck. This guy just learned a tip which hopefully will help him get a better view of a candidate.