Well....if you're gonna break it, do a good job, and Jean did just that. I also have never seen a valve stuck like that in a cylinder. That's some crazy Physics going on there.....
Judging by the amount of corrosion on #7, I think this engine may have had a coolant leak prior to #1 letting loose. I am guessing this engine sat all winter and then was taken out to raise hell. Fine and dandy on an engine that does it often, no so good if it sat all winter. May have had dry valve guides that were not working freely and the valve stuck and got clobbered.