"Mmmph, not sure," said Casey around the apple slice he popped whole into his mouth. "Uh, musta moved it when I was lookin' for somethin'. Forgot to put it back. I'll grab yours." With that, he sprinted towards Bones's room.

He'd put the regular kit back when Bones wasn't watching.

...And he may have hung back a little bit while Bones explained what happened. Half because it had been bad enough hearing it the first time...and half because he wanted to see if he could hear what Greg was saying to Rose through the wall (he couldn't.)

Oh well, he brought the kit back once he was sure Bones had finished and grabbed another slice.