If it was the case that 'stopping quickly from speed' ie either killing the engine completely or coming rapidly back to neutral from WOT (both of which are perfectly feasible and forseeable situations) was sufficient to drive water up the leg into the pots then I would imagine the manufaturers would have put some kind of reed valve in there to prevent damage.
Besides, even if the engine simply stalled with one or more exhaust ports open (without turning backwards), creating the possibility for water to enter the cylinders, I would be surprised if it would re-start at all. Even then the water would simply be ejected back out of the exhaust port from whence it came when the engine was re-started.
Looking at the photos in the OP there is evidence of corrosion in at least 4 cylinders.
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