That is strange. Perhaps something else has damaged the coating and that is why you are now seeing what looks like pitting. I agree with what everyone has said. It could be tool marks.

I have been carrying my G27 for the last 17 years and of that i've been using a trigger guard holster and clip draw for the past 8 years. My g27 is always against my skin and being sweated wet in my cycling jersey and there are no signs of pitting on it. The clip draw shows more signs of wear and tare than my G27.