Turning corners during Sion ult

I just had an ARAM game where the enemy Sion ulted and passed next to a downed turret and managed to make an almost 90 degree turn behind the turret remains.

I think unit collision had something to do with it, but I'm not sure and I don't have a replay of it.

If it helps in replicating the bug, there were minions on the way to the turret remains just as Sion reached it. And I believe he was already turning into the turret's base, he was running towards the upward inhibitor turret in a straight line on the left side of the turrets.