Definition of mental disorder

In a recent Tribunal, the judge asserted that (in an asymptomatic patient who had one psychotic episode some years ago) a brain lesion itself constitutes a mental disorder for the purposes of section 1.
He based his assertion on the quote from the 2007 Explanatory Notes reproduced in Jones at 1-032: “Disorders or disabilities of the brain are not regarded as mental disorders unless (and only to the extent that) they give rise to a disability or disorder of the mind as well.”
Is he right? Are there contrary authorities?

Thanks for this Andy. That’s a massive assertion by the Judge. A lesion could surely have a number of definitions.

Purely clinically, once you start looking at ‘normal brain structures’ they are pretty quirky, and have all sorts of abnormalities that are not expressed as disorder. Going on brain topography or fMRI to evidence mental disorder with no symptoms is a shakey path to tread. I do love a reason to quote an IgNobel prize winning bit of research tho.
IgNobel Prize in Neuroscience: The dead salmon study - Scientific American Blog Network