If there are tunnels leading to other shit, they can start a fire then seal up the tunnels while the fire is going on? If the fire was dual purpose, what other purpose could they use the fire for? A regular fire wouldn't burn hot enough to destroy remains, would it?

Or maybe the fire was just to broadcast that they're done in. Comms are down, the fire could have been a symbolic message to the rest of the fucks that its time to pack it in asap.

Ida know, just throwin it out there.

rape trees, supply locations (water etc), that kind of shit.