Or etching from tree sap OR bird-droppings that got washed off in the rain, but left those very small areas of etched clear-coat behind.
A judicious hand-application of a compound may help IF it is not too deep. The fact that you mentioned it was glass-smooth tells me is not that deep and doing it by hand on an applicator pad is just a suggested, east-to-do first step.
I doubt an OTC scratch-remover would be "abrasive" enough to remove this by hand, BUT you COULD try this first if you have some in your detailing product "stash" and feel so inclined.
I know you are trying to resolve THIS particular problem and what may be its root-cause.
Driven vehicles are subject to a host of paint-staining/etching causes, from road-striping/marking paint, freshly-poured pavement concrete and asphalt specks, to industrial fallout and associated acid-rain, hard-water marks from landscaping irrigation, and the fore-mentioned tree sap, bird-droppings, and insect bug splatter.
Concrete splatter is particularly "difficult" to remove, as is yellow and white road-striping paint specks, especially if it has been there a while. But that`s what good detailers do; they resolve to exterior paint problems. The key to this is:
1) having the correct specific detailing product to remove or dissolve the offending fall-out,
2) the tools to help using those products
3) the knowledge and expertise to use those products and tools, along with the perseverance to try using more-than-one approach or even outside-the-box thinking.
Good example is using plastic razor blades or plastic scrappers to remove larger road-paint specks or excessive pine tree sap from an exterior surface. I don`t like doing that, BUT sometimes its the most-efficient first-step.
Another is using regular Coke-Cola (not diet) to remove concrete specks. The phosphoric acid and corn syrup sugar in Coke helps dissolve the concrete.
