Seeing these words, Onogi was visibly stunned, then he guessed what was going on.
Deidara had already been rescued, most likely during the chaos when Onogi used his Dust Shield.
Su Xiao certainly wouldn't rescue Deidara himself, and if he had, he wouldn't leave the words 'Bu Wang was here' on the ground. The one who would do such a thing, or rather, the one who would do such a dog-like thing, is undoubtedly that fool Bu Bu.
Bu Bu Wang had been lurking in the stone house above, and once he received Su Xiao's message, he infiltrated the underground prison.
The reason Su Xiao was hit by the black stone spike was because he was creating a safe path for Bu Bu Wang, thus his space for evasion became increasingly narrow, and eventually, he was struck by Onogi's 'Super Weighted Rock Technique'.
From start to finish, Su Xiao's goal was never to attack Shuyan Village or kill Onogi. If he wanted to attack the village or destroy the shadow, he wouldn't be acting this way.
