It could be anything. That car could have been parked near a dealers bodyshop, and had overspray from the cut-in area hit it. It could be overspray from someone painting a building nearby with a power sprayer, etc.
I would take it back to the dealer, You may be able to get it covered under warranty.
A friend of mine and I both have F-150s. He works in a bodyshop, and I recently asked him to help me wash, claybar/buff and wax my truck, and we noticed that first my truck, then his had these small reddish brownish spots in the paint. It was harder to see on mine since its a goldish color, very close to the Saints gold, bit his is white. He had no idea what it was either. We eventually got it off the paint, but it was weird. It looked a little like rust spots. It couldnt be rust though, it was on the hood, and F150 hoods are aluminum.