My thoughts exactly. Doesn't seem like Nayuta actually saw them kiss. They were already done when the door opened.
She could just saw Yoru stealing/hijacking Asa's body and did something.
Can't wait for the update though for some real conflict/explanation on what's going on.

Oh, here's a thought. Nayuta also doesn't know Denji is Chainsaw Man, and since she can't know anything about the Asa/Yoru situation, she thought they were an actual theif. She thought Denji was being attacked by a robber.