cpt,
This is an entirely unofficial response, and not to be confused with any official response from any authority:
I have seen these kind of small pits on the blade surface, usually in the filler material that is a kind of putty/body filler, almost like a spackle. The areas where the airfoil contour are smoothed in seem to have this imperfect system of popped bubbles, most quite small, none into any actual structural material.
I believe they are quite normal, and probably cause by a mild ablation of the outer layer of the filler (rain? light dust/sand?) that exposes the pits caused when the slightly bubbled material is worn down a bit and the bubbles are opened at the surface. I have seen this especially near the tip caps, where this filler might be used more.
Certainly, this is not a sign of lightning or static electricity, which would show on the sharp ends of the blade airfoil where the charge leaps off the blade. It is also not a sign of exhaust heat, which would cause a fairly large bubble/void to form directly over the exhaust, with a diameter of perhaps 5 or 6 inches (I was the first on the planet to burn a blade, thank you very much!) And I seriously doubt that it is the product of someone's grinder, which should be nowhere near a fueled aircraft, else the specks will be your least worry, and a big fireball/barbecue pit where your helo used to be should be your biggest worry.