Sion Kalista Bug

I was in a game playing as Caitlyn in the bottom lane, and the other bot duo was Sion and Kalista. Sion would ult (I wasn't in lane, but I saw it while walking back to lane) and he would hit the wall right past the 2nd tier turret, then reappear in lane around their first turret. Not sure what was happening, but our whole team went wtf, but we had a laugh about it. I think the Sion and Kalista knew about it before though, because in all chat they'd said "shhh this is supposed to happen."