RDT, Sadly, I cannot tell what I'm looking at from the pics. I see white horizontal marks on the fender well, and a horizontal white near the roof line. But I can't tell if that's a reflection of clouds??
Oxidation would not happen within one week on single stage paint, never the less clear coat. It would take years, with no protection, no maintenance and lots of industrial fall out eating away at the finish.
Can you get some better pictures at a different angle to determine what it is we're looking at vs. reflections? Perhaps take an LED light and hold it to the surface while shooting the pic?
What does it feel like when you rub your hand over it or a baggie test?
Could it be bird drippings that smeared?
Edit: Ok, I think I see the faint clouding in the photo... Sometimes it helps if one could edit the photo and draw a circle around the area of concern. You say you didn't have it covered, but it really looks like moisture buildup on something that left an impression... i.e. leaves that fell and got stuck to the finish, or someone leaned something against the car, or the cover left an imprint. If it wasn't there a week ago, and now it's there, I doubt it's permanent.
You should start with washing the effected area.
Use an ultra-fine poly clay with a liberal amount of clay lube, see how it looks.
Either, compound/polish, AIO or go right to wax/sealant (all options for you to explore) not telling you to do all, just what you feel comfortable with. Whatever you do, perform the least aggressive first in a test spot.
But I'd be interested to see how it cleans up after washing and clay.