Not every inch of a bar of steel must be good. There are a good many reasons that could occur during several points in processing. Inclusions are not uncommon. It's a risk anyone grinding on a perfectly good bar can find. It's a little more risky on pattern welded stuff but then we are sticking materials together in a way that can cause anything from big to small inclusions. It could be decarburization at the edge during the heat treatment cycle (done badly), or an edge is built from what looked like good steel but was decarb on the billet during forging. Rusty oxide pitting, sure that too. Poor quality control, the final inspector just got fired and took his revenge.
Here we are doing a forensic evaluation...RSI in action.