The way my vet described it to me is that once the stone completely blocks off one of the kidneys, it can cause the other kidney to go into acute renal failure. It happens in such a short amount of time.
You did the best thing you could for him by giving him a peaceful passing. Rest well, little guy.
He really did like to surprise people with some of the goofy things he did and he managed to convert a few of our friends who were guinea pig disbelievers into lovers and new owners.