My guess is that you have pin holes in the cyl wall from years of rusting on the inside. aka water jacket side. When you honed it, it hit that critical thickness and stared to leak coolant/water. into the cyl/combustion chamber.
I bet, that if you took a flapper wheel to the dent in the bottom of the bore........You would go thru the cyl wall. aka paper thin.
Hope you find a sonic tester
