Mob controlling a boat

I was testing things in solo with boats and stuff, and I actually managed to make a Zombie control a boat (he was using one of the paddles and was turning around) .
I tried to reproduce it, but I didn't find how I managed to do that.

The screenshot isnt really accurate, but you can see that the zombie in the top left side has his left paddle in a slightly different position than the other ones. He was using it. I agree that this isn't very obvious, but I can assure that he controlled it.

PS : I'll continue trying to find how I did it.