It also says: “There have been no such studies done on non-clinical plurality yet, but interest has been growing in the field.”

It is also saying that DID is one type of plurality, it is not calling it the only type.

Not all of us have the clinical/medical type of plurality, DID, OSDD etc etc.

If you’re genuinely interested then: https://pluralpedia.org/ explains many more types. Especially this page, gives a basic starter: https://pluralpedia.org/w/Plurality