If I tried to speculate that the grind lines were caused by being ran over by a truck during production, I would have been promptly refuted. When I heard it being suggested that the edges are CNC machined, it might as well have been suggesting that the truck is grinding them.
Then people started arguing in favor of (the truck) being a possibility. No it isn't and I wont pretend it is.
As an added data point, my first K390 SE P4 (purchased as soon as it came out) showed the same pattern of grind marks as the OP's, while the last one I bought (after it was discontinued) they are barely visible. That suggests, at least to me) that a new serration wheel was made for the model, and wore down over time and use.
