ENFP here!
@
(you need an account to see links) I think there is a big element of it being how we perceive ourselves. The website's calculating algorithm doesn't know us personally.
When I know the categories, I have to be careful to give myself enough time between tests to try to answer accurately and not how I want to be sorted -which has to also be its own trait thing. Gryffindor, perhaps, LOL.
With all personality tests, I'm pretty passionate about them being descriptive, and not prescriptive. An informed person can know how they trend, which can in turn help set good healthy personalities or look outside the box and grow as a person.