This just happened to me the other night.
I’m in a dispersed camping spot in a National Forest. It’s not crowded. I go to sleep around 9:30PM and wake up at 4:30AM to someone parked right next to me. There’s no trees between us and no possible way that they did not see my car.
As I drive out of the forest I pass dozens of empty spots.
This has happened to me twice. Who are the people who do this? There’s no rational explanation for it.
I think your shock and confusion is 100% valid. The whole point of trekking out to remote camping spot in a National Forest is usually to get the hell away from other people, is it not? That seems… rude at worst, and ignorant of them at best.