Paint is a chemical. Once hardened is can be damaged by mechanical removal (scraping, abrasion) or radiation (fading, delamination) or chemicals. Older cars can be seen frequently the celar coat coming off. Had a mustang yeas ago with an organic base paint (as they all are) over a water based primer. In 14 months the whole car was in primer. For a change to have been observed over a short period of time my bet is on a chemical exposure. E.G. someone dropped acetone on the fender. Intense sources of radiation are most unlikely.
