Metals are made of crystals, they usually defourm along the grain boundaries and fatigue cracks also grow along them. By eliminating those boundaries you reduce the chance for fatigue cracks and make the overall blade stronger.

That is a very odd failure so not 100% sure. If I had to take a punt I would say the nozzle jammed from the mentioned heat creap issue, eventually the silk pla broke in the extruder as it’s very brittle, combined with retractions. It then was then able to work its way out and make some noodles for you to enjoy.