I've no idea if that is how it was done really.....Bloody clever though.
I don't think there is much universally accepted proof this is how it was done, but like you say, it's a very clever and well thought out system.
You also don't need the hundreds of thousands of slaves originally thought to have built the Pyramid by the traditional method, but a mere a fraction of the labour force with this water method.
It's also widely accepted by egyptologists that the stones were transported down the Nile on barges in the first place, having been quarried away from the Pyramid site and this new water method just expands on that idea.
Theres also a growing theory that some of the stones were cast in place. Sort of like pouring in ancient concrete.