No, but everyone in Impossible Spell Card is cheating since they're (story-wise) using spellcards that are impossible to dodge (which's also against the rules).
Alternately, Seija's just being an amanojaku again, and calling someone who's very straight-laced "a cheater" because everything she says is a lie. (Like she just called Sukuna "rotten" when she was trying to reach out her hand to help her.)
