I think what he meant by "topography" was simply "surface colour". I.e. darker surface creates darker shade of blue and lighter/more leflective surface creates lighter shade of blue, giving off an illusion of heat map.
The problem I have with that, is that if this surface colour is the "final" visible colour, which you see in "combat mode", after all layers have been composited together, then the exact same thing applies as with topography: If a certain hill is blue for both, say, frutexa and tussock, then the pattern of variations of blue on that hill should be identical with both filters, which it
can be in some cases, but by no means
all.
If, on the other hand, e.g. only a subset of layers produced the blue and its variations, there
could be different patterns.
If one took this to the absolute extreme, and imagined there being a dedicated layer for each and every element (which I can not imagine to be the actual case, to be clear), and you had e.g. a discrete, one-shot, shape "stencil" for sulphur somewhere, imparting a yellow tint, interacting with a tiling global texture that imparts red for iron, and a certain plant would only grow where it can have both, that could produce a two- or three tone map, depending on what one do with one's truth tables. There could even be NAND terms, e.g. ruling out proliferation where there is copper.
(A strict truth table producing a single boolean would of course only produce blue, without any variations...)
Height
does seem to play a part in many filters, often producing sea-like blue regions, where mountains poke up out of it, above a certain threshold, but that does not stop the map from blue-ing huge tracts of land which are entirely the wrong elevation for the filtered plant, and where it will absolutely not grow; Quite possibly this could just be a side effect, rather than elevation actually being an influencing term, caused by procgen rules mimicking geological factors favouring certain elevations, such as a crater-producing meteor impact exposing and ejecting matter from deeper strata, or mountains being bare rock.
Another thing that could explain the difference, is of course simply that the procgen could at any given moment pull different mipmap levels for each filter...
