Useful languages can succinctly distinguish things which are qualitatively quite different. Describing everything in the world as "intelligent" sounds kinda cool and Zen, and may reflect some peoples' worldviews - but it also make "intelligent" pretty useless as an adjective.
Intelligence is not well defined enough for a succinct distinguishment. At least, not colloquially.
But also we're in a context where acknowledging the intelligence of other life forms is pretty radical so distinguishing them as 'lesser' than human would be precisely opposite of the point. The baseline world view is that human intelligence is magically different than other animal intelligences.
1) It's a poorly defined word that means different things to different people
2) The word "mechanism" perfectly describes what it is
At the end of the day it's just using the detection of food, to switch from "tumble" (try a random direction to find food) to "run" (assume we're near, or in, a patch of food, and move forward to consume more).
If "hot" described any temperature from "the dark side of Pluto" to "the core of a brand-new neutron star" - then how useful a word would "hot" be, for communication between humans?
It's also seems odd to call it "baffling" when they 100% understand how it works!