Those look a lot like the rust spots my stainless steel table knives get in the dishwasher (or used to get, before I started hand-washing them) - it's like a little bubble of rust that you can remove with Barkeeper's Friend or similar, but it leaves a tiny black pit that will rust again when exposed to the same environment.
I don't know if it's an inclusion in the steel that's rusting, or if the act of rusting creates the pit in the regular steel that's then susceptible to rusting again.
I don't know if it's an inclusion in the steel that's rusting, or if the act of rusting creates the pit in the regular steel that's then susceptible to rusting again.