Sounds like pitting to me. The rust ate a tiny crater in the metal. Happened to my 1911s slide. U can probably search youtube for how to refinish metal surfaces. Being that its a cheap pistol, it may be a project you may get your hands dirty in. Otherwise, someone more experienced may need to do this. I imagine the job would cost more than you paid for the firearm, though.
Concealed Carry in Illinois!
The 50th state to recognize the Bill of Rights...