Towers not being destroyed

I was playing a custom aram with some friends to just fool around, and we were done so instead of surrendering we all quit and one guy stayed and finished the game. We decided to go back in and mess with him a bit though and when I reconnected I saw that he pushed the lane a lot , was attacking my inhibitor, but the inhibitor tower was still up (before I left only the first tower was destroyed)

It wasn't attacking anything but it didn't crumble like it's supposed to. I haven't tried to replicate it so i don't know if its possible to do so, just thought i'd share