Thank you for the additional information.
Two things I have gotten out of this. 1st, his rebuild only lasted about a week. 2nd, he cannot tell (or wont) tell you what it failed.
I don't know you or him, or what your relationship is with him, but in the industry, neither of those conditions are confidence inspiring traits. Is he repairing it for free, as in did he warranty his work? It is hard to think this is anything but a failure that he is responsible for. No matter, if you trust him, that is all that matters.
One thing that is imperative, he needs to determine the cause of failure and correct it so it doesn't do it again in another week. I would really like to see a bunch of pictures of the block and cylinder, head, piston, rings, connecting rod, and anything else that shows damage. That could be real beneficial. And also if you have any of the failed parts from the first failure too.