As a general bit of information.......sealcoating usually has about 5 pounds of silica sand per gallon to aid in traction, otherwise the stuff becomes like ice when it's wet. Silica sand is also a very aggressive media used in sandblasting.
I would be VERY EXTREMELY cautious doing anything that involves repeatedly rubbing the spots. I'm having bad visions of the spots being gone, but a whole bunch of swirlie scratches.
Personally, if it were me.......I'd find out if the neighbor did it, or more likely, had a company come in and spray it on. If a company put it on then I'd hold them responsible and demand a re-paint. Sue, if need be.
When I put this stuff down years ago, you occasionally had something go wrong, and wind does blow the overspray around, but there is NO EXCUSE for getting it on a vehicle!