Thanks @Emily Barnett - that last message helps me understand where you are coming from.
I respect your perception of this situation.
I do however think that people won't be confused by the niche.
Could the description be better - certainly... but I think it still gives a good sense of what kind of photos are intended to live there.
The main issue seems to be with your binary approach to candid vs portrait, with a moment where one becomes the other, and without room for shades of grey between them. I think many professional photographers, and most non-professional ones will be more flexible and understand the intention of the niche.
I think it is safe to say that most people don't see a portrait photo as necessarily meaning contrived or posed. Portrait, for most people, just means a photo that 'portrays' someone... Even though you have a more strict definition, can you maybe work with the fact that many, and perhaps most people don't?