The breakage was due to a pierced primer. The gas came back through the firing pin hole, drove the firing pin back and broke out the part of the breechblock that retains the firing pin. This is normal with a pierced primer and the reason they went to the fluted firing pin, even though that is not always enough to prevent damage.
The breechblock striking the frame had nothing to do with the damage.
Pierced primers could be due to the firing pin or the primer itself, but in this case it looks like a combination of excess headspace and maybe a weak firing pin spring, probably combined with high pressure.
The flattened primers at the top are classic. The excess headspace allows the primer to back out and spread out under its own internal pressure, then internal pressure in the case pushes the case back over it. Meantime, the primer has tried to back into the firing pin hole and apparently did so, since it blew out and let gas into the breechblock.
It is an article of faith among Luger collectors that the guns are carefully fitted. That includes breechblock and toggle lockup, which controls headspace. Swapping parts, or working on things to smooth up the gun can have nasty consequences, though almost always damage is limited to the gun.
HTH
Jim
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