Makes sense, though I'd say that my brain still has a concept of up even when looking down at a fretboard. More so when I'm holding a guitar and looking horizontally outwards (reading from a screen) - my brain knows which line/string is closest to the ceiling and which is closest to the floor. If I'm copying a chord from another player (very common) then I'm naturally doing the horizontal transposition but never a vertical one (ok, lefties playing a right handed guitar backwards, but that's rare and confusing in itself).

As the page seems to be a resource for inexperienced players, and as there's already a lot of confusion between up/down for notes and spatially on a fretboard, making things blindingly obvious seems like a bonus. Even something as simple as making the "strings" different widths would give someone more information to spatially orientate themselves.

edit: I guess my brain is far more wired up to deal with things flipped horizontally (looking in a mirror, being shown how to perform an action by someone facing me), but I can't think of anything where I have to deal with objects flipped vertically (rather than rotated 180). Interesting to find out this seems to be a "me" things rather than common/obvious one :)