[Vicegrip]

Making the determination that this was a direct result of a procedure failure would require more than looking and thinking. Did you contact the tin kickers?
I did some digging after looking at the parts and found that this is not an unheard of failure on a highly stressed point. Your hub failed in the same manner that other hubs that were not beaten on have failed.
2. You have 20,000 high stress miles with some to most using oversized track compound tires and rims that Porsche has in print recommend not be used.
3. There are no reasons to beat on the back of the hub other than short cut service methods. On the other hand look at what the part is built to do. It 100% holds a rear wheel that holds the car up and transmits all motor and braking torque energy as well as all cornering G loads and wheel impact shock. Hammer hits are not the same to this part as they might be to a knee cap. It failed at the weakest point as well. My guess is that they might have been struck while a puller was also being used. Some hammer hits can induce a shock wave that makes interference fit parts release under tension that would otherwise not dislodge them. Note the angles of the ball-peen impact dimples. Some swing angles are directly edge to center some are oblique. This pattern might come from the hub being struck while the puller in in place and preventing the hub from being spun.

I don't know what happened to your hub at all but here are people that can inspect, test and determine the failure mechanism.