OK to give the PO some benefit of the doubt.......
As the plug was being inserted into the plug hole it was not aligned correctly and the electrode caught on the top thread while at the same time some side load was applied while pulling it back out for another try???
A piece of debris managed to get past the intake valve, whack the plug, and make it back out the exhaust valve with no other damage???
That cylinder was way lean for a little while at high RPM and full throttle and it got hot enough to soften the electrode?
Yes now I'm grasping at straws.
Well OK I did say some benefit of the doubt ........