Yeah, I've found it very confusing too.
Does it mean I can improve any score (BSE) or only the score from my Profession (class is a profession, right)? So if I'm a Botany Priest, can I improve only Erudite or also Brute and Skulker? That makes for quite different gameplay!
Minimalist design is one thing, but confusing design is another. How do you guys play? Do you allow increasing one score or any score?