I believe it indeed was. I love these "Autological" words[0].
My favorite by far is the acronym ETLA (Extended Three Letter Acronym), which of course had to be invented because FLA (Four Letter Acronym) is not autological[1].
I also thought the use of "construct" to mean "abstraction structured like diagnosis which doesn't describe a pathology" was not itself an improper noun, but is probably how they get started. If everyone in the field started using "construct" that way, it would become an improper noun.
I actually think "construct" much like "disorder" is a kind of marker for an improper noun. Both are so formal as to suggest that "adjective adjective construct" is a formal term. Such improper nouns, I think, are less insidious than improper nouns without such a marker. Because they are easier to detect.
If the "highly sensitive person" were instead called the "highly sensitive personality construct" it would be much less confusing as an improper noun. It is clearly unwieldy here, but that is partially down to construct being too vague, and presumably down to me only spending 10seconds on the name.
As an example of how "disorder" helps suppose that "Persistent depressive disorder" were instead called "Persistent depression". That would clearly be much more confusing.
Improper nouns are just starting out in life, with time they will become improper-nouns subsequently impropernouns and then if sufficiently misunderstood by enough people they might become propnouns.
My favorite by far is the acronym ETLA (Extended Three Letter Acronym), which of course had to be invented because FLA (Four Letter Acronym) is not autological[1].
[0] https://en.wikipedia.org/wiki/Autological_word
[1] http://www.jargon.net/jargonfile/t/TLA.html