The engine block, the largest and heaviest piece of the engine, is made of either cast iron or, in most modern cars, aluminum. It has to be strong to withstand the forces of combustion and torque and everything else going on in an engine.
That makes breaking a hole through part of it an impressive feat. Usually it takes something like a piston rod breaking for anything to have enough force to make break through the solid metal. I’m not sure what happened with the engine, but it was apparently mechanically fine, it just had this hole in the bottom of the block. Luckily it was in a replaceable part, so it didn’t need an entire new engine block.