Island Park Campground is a pay to use campground. It gets quite busy in the summer, especially over long weekends but definitely is starting to fizzle out with it getting cold at night, kids being back in school and no long weekends any time soon.
Tent Mountain Road is about 15 minutes south of Island Park Campground so i doubt anyone from the park would have even seen them. Where they were, no campsite and grounds were located. they could have been using a fire pit but those are few and far between out there.
My husband is Native and he grew up with stories from his grandfather about how to never go into the woods alone because there were entities that wanted to lure you away and take you.
I got the images below from Google Maps. This is Tent Mountain Rd, it doesn't follow the whole road but it goes down it a bit.