Yosemite and Yellowstone get mixed up all the time. It would not be unusual for someone to send a quick text like that and accidentally write the wrong place. Yellowstone is a stones throw from grand Tetons, literally when we visited there 2 years ago we drive out of one park and within an hour or so we had entered the other. I wouldn’t even really know they were separate except for the entrance stations. Yosemite on the other hand is a few states and an entire full days drive away. 2 years ago we had horrific service in Yellowstone (I had 2 teens with me, believe me I heard non stop complaints about the lack of service!) This is also bear country. I’m starting to plan an backcountry camping trip next summer in grand Tetons and they are serious about bear precautions (rightly so). I would sadly imagine with any body left out for 3 weeks time it will be very hard to determine what actually happened, unless it was a gunshot, which I highly doubt!