I think you might not be interpreting that in the way that it was meant.
Perhaps consider: what things would someone who calls some things “mental illnesses” and not call them “physical illnesses”, contrasted with the things they would call “physical illnesses” and would not call “mental illnesses”. What name would you give to these two categories?
I am reminded of a conversation I had with my dad, perhaps 5 years ago, where he referred to something as a plant, and I was confused because he meant that in a way that excluded trees, while I hadn’t interpreted it that way. Now, of course, in the technical sense, trees are plants, being members of the kingdom Plantae. But at the same time, if one is in an area with 5 trees, and a plant which is not a tree, and someone tells you “look at the plant”, the pragmatic way to interpret what they mean, is that they want you to look at the plant (i.e. the plant which is not a tree).
Scott Alexander said (as a paraphrase/snowclone of Christ’s “The Sabbath was made for man, not man for the Sabbath.”) “The categories were made for man, not man for the categories.”.
Edit: small formatting fix