Not to mention.....since Thermal vision makes non heat based objects blend in together, how does even the Predator notice the traps laid around the camp?
The script has a mention around traps/trip wires in particular showing up in the Predator's vision (or referenced as the 'Observer' in the script).
36 EXT. JUNGLE - OVERHEAD - ALTERED P.O.V. - DAY 36
SEEN THROUGH HEAT-SEEKING VISION, FOCUSED ON Blain
and Mac, lying in the grass below, their bodies
outlined in LUMONOUS AUREOLES. The Observer SEES the
NETWORK of TRIP WIRES guarding the approaches to the
machine gun nests. The wires GLOW as if ELECTRIFIED,
standing out in hard-edged relief in contrast to
the jungle foliage. He moves higher into the forest