I don't see where that could happen, though I may be wrong. How would a spark failing to fire cause the piston to travel higher in the cylinder than it normally would? And, don't we have a spark cut-out type rev limiter? When that kicks in you don't have the pistons impacting the plugs.
I would seem to me that the center eletrode and it's porcelain insulator would be much less robust than the grounds and would sustain more damage than the grounds if struck by a piston, which from the pics doesn't seem to be the case.
Looks more to me that there was something bouncing around inside the cylinder, broken ring, or even a sheared piston. That could go along with the excessive cranking - the starter puts out a lot of torque and can easily break rings and pistons in some circumstances.
There were failures of some of the cylinder lips on earlier cars, always cylinders #3 and #4 attributed to the block torqueing like this:
Wonder if something like that occurred?
Doesn't sound like hydro-lock though. It's usually the pistons which take the beating from that. And, once the plugs were pulled, all sorts of gas/oil/coolant would have come gushing out.
A borescope would give better information, but the engine would need to be torn down anyway, so it may not that helpful either.
Everything here is a guess. The only way to know for sure is to have a pro check it out.