Try it on your phone - if you type a capital "Y" you get lots of suggestions - but a person really needs to type the first three letters to get YOSemite vs. YELlowstone (and if you type YEL you'll get...yellow before you get Yellowstone).
I don't buy this as an auto-correct situation. I'm active on TripAdvisor and people confuse the two parks ALL the time. They want to fly to California for a 5 day trip and "see Yellowstone."
I've been in Yosemite recently, and heard a couple asking the ranger about the geysers. Yup. They are both amazing parks, both are on everyone's bucket list, apparently, and they are definitely confused.
What's interesting to me about this couple's supposed trip into Idaho/Snake River area is that it was and is getting fairly nippy overnight...not a good time to just sleep out on a tarp (but possible - it would be uncomfortable in just a T-shirt and shorts on top of a tarp, at 40•. IMO. One night, maybe, but you'd need quite a few calories so that your body could use all its mechanisms to keep you warm enough. Even at 45•.
I also note relatively placid black bears are out all over the Sierras now in their hyperphagic phase trying to eat everything around prior to hibernation.
I would really be worried about those much more aggressive hungry beasts in the Wyoming area in a hyperphagic state, especially if he was foraging for their berries, etc. What do you call those WY bears now? Oh yeah. Grizzly Bears