I've been mulling this over. There is no way they could have ended up in Boquillas, Mexico after wandering lost for many days. Simply no way. The brief news reports state they were in "healthy" condition. Was it a staged disappearance? Only Hector Flores knows.
My impression is they were located in Boquillas del Carmen, Mexico.
The southern end of Old Ore Road is close to Rio Grande Village, a major developed campground in the park accessed by a nice paved road, and also the location of a legal crossing into Mexico.
The tiny village of Boquillas del Carmen, where Hector and LF were found, is a half mile from that crossing, and welcomes and is economically dependent on tourists. I can't imagine Hector and LF being there without most of the residents knowing, but who knows where they were actually staying.
The park service has a page about visiting Boquillas:
Visiting Boquillas, Mexico
Boquillas has it's own website in English:
Boquillas Internation Ferry -- Your Ride to the Other Side: What you need to know.
Also, the Rio Grande is incredibly low right now. It would likely be easy to wade across.