Overblown.
While cleaning out stuff is recommended, pretty much everyone comes into Yosemite in a vehicle that's been used to transport food at some time. Maybe there's a soda spill or a few crumbs. Yosemite's "bear aware" videos actually show people merely removing food wrappers and soda cups, but it looks like minor smells would still be there. They recommend vacuuming the carpets and upholstery if you can, but you don't have to go overboard.
In the backcountry pretty much everyone stores food in their packs, but makes sure they're in the bear canister when setting up camp. I certainly didn't rinse off my pack, and there was a bear going into someone else's camp which didn't actually go after anyone's food.
While it could be bad for you if a bear breaks into your pop-up camper, that's not the main concern of the NPS. Their primary concern is if a bear actually scores food and learns that breaking into vehicles pays off compared to looking for natural food sources.