Those little triangles are campsites. The campsites are numbered. It's possible you have to get a permit for the exact number. If one or both of the pair were overnighting at one of those campsites, LE would know because they would have had to register all their ID information. Rangers at National Parks keep track of everyone in the backcountry. Rangers sometimes come by to make sure you aren't building fires, "leave no trace", etc. Plus, other campers keep an eye on things (experienced folks are very particular about how the backcountry is treated, so everyone can enjoy it).
I've been in a situation where all backcountry overnighters (including the resident Ranger) had to leave Sequoia NPbecause of a series of blizzards (in early September!). A helicopter came by regularly as we hauled ourselves over a high pass above treeline, with a Ranger hanging out the door counting everyone, to be sure that everyone got out. They were missing one backpacker registered to that area, which caused some concern.
Long and short: NPS has information on whoever was in the Grand Teton backcountry overnight. Maybe even just day hikes (in wilderness areas, you're required to register at the trailhead and carry a ticket on your pack, even just for the day, but I don't know if this is true for National Parks).
And yeah, if they're pointing to a cluster of campsites, they have quite a bit of info from various sources.