Yes, the mana reduction is not considered a status effect. Rather it is a skill side effect, like draining health from the enemy is (e.g. Leo’s skill).
However, you are right that the blue and yellow reflect skills from Mitsuko and Ursena will still reflect them.
And it gets even more confusing!
The dispel – for e.g. Sonya’s skill – is not reflected when she hits Mitsuko with her buff active; Sonya hitting Mitsuko will get her damage reflected back at her, but she dispels the blue reflect status after.
So idk… maybe it was too run-of-the-mouth to say “status effects, special skill effects and blah blah blah…” ¯\_ (ツ) _/¯