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 don’t see where they said they camped in their car. They could have easily parked the car at the site and then set up a tent, or like we do, towed a pop up camper there.
After rereading they do mention they’re at a campground. I focused on the ‘dispersed camping spot’ phrase.
The only conclusion I can come to is OP uses different camping terminology than I’m familiar with. For me ‘dispersed’ can have a broad range of meanings but always means ‘not at a campground’.