Yep, there's not really a good explanation of what beginner/intermediate/advanced means. Also it seems interactions are rated--- meaning what? Ability of speaker in said language? Interestingness of speaker? Whether they are normal?
Re. ratings: We simply ask you, "How was your conversation?" Based on whether you superlike/like/dislike, we can pair you up with that same native speaker more often, at the same rate, or never again.
Hope this helps!