That statement being that all mental diseases are physical diseases. They aren't. Sure, some mental diseases are caused by physical structures within the brain being damaged or malformed.
However, some mental diseases are learned/acquired from life circumstances (where they did not exist before the acute event or chronic environment). Your assertion that they are one and the same doesn't really line up with that.
From what are you basing this on?
~Jeordam
Saving the Princess, Humanity, or the World-Entire since 1985