I don't doubt for a second that it could be done. I just doubt that it was done by accident. In the 60's I read of some tests done after the war on Arisakas that involved welding a rod in the bore and firing the rifle with a normal round. It evidently blew the rod out without much trouble and no further damage to the rifle.
To me the rifle described in the cartridge conversion sounds like a similar test and not something a knowledgeable gunsmith would do by accident because of the difficulty in getting a 30/06 reamer to enter a 6.5mm bore. I may be wrong though, even as improbable as the rifle conversion seems to be.
