That's odd... [Yasu murmurs. She taps her chin, rearranging all the pieces that Dylan, Adorabat, and Emma have presented in her mind... and snaps her fingers.]

Maybe...

If you were splashed with a bucket of paint at an angle where it would make a silhouette against the wall, almost none of it would get on your back. Right?

Thinking about it this way, I wonder... was the culprit trying to make it seem like Thomasin somehow made the silhouette? There aren't many other reasons I can think of to clean the paint specifically off her back, but that just raises more questions.