What Wendy is saying, is that humans only recognise the directions as different out of necessity.
We live in a world with 3 spatial dimensions and 1 time dimension. Having one time dimension means that things can move in one spatial dimension at a time. That dimension we call "forward" and "backward", and because of that, humans have a "front" and a "back". I call this dimension "frontal".
Next, we live on a planet which has gravity. Gravity also operates in one dimension, which we call "down" and "up". Because of that, humans have a "top" / head and a "bottom" / feet. I call this dimension "vertical".
This only leaves one dimension remaining, which we call "left" and "right". It is the easiest to confuse because there is nothing special left about it. Indeed people who have trouble with their directions (dyslexia for example) generally struggle specifically with left and right as opposed to other directions. You are far more likely to get 'b' and 'd' confused than 'b' and 'p'. Languages of the world are variously written left to right or right to left because at the end of the day it doesn't matter, and some are written top to bottom, but none are written from bottom to top. Indeed perhaps the fact that we are so bad at handling left and right explains why when we look in a mirror we think left and right are flipped (they aren't: it's actually forward and backward that are flipped, while our brains are thinking of an imaginary space that is rotated 180 degrees in the vertical axis). I call this dimension "lateral".
You may now think that, if humans were to go into space they would still be able to identify "down" and "up", and indeed they can, but only because they brought their bodies with them, which were still designed for a with-gravity environment. But if humans lived in space from the beginning, and noone had ever experienced gravity, there is no reason for the body to be shaped the way it is: it would make more sense for it to have a high degree of symmetry along the frontal (forward-backward) axis, looking for example roughly hexagonal or circular from the front. And then, these hypothetical humans would not have any concept of what "down" and "up" were, and would be more likely to think in polar coordinates, "how far out" and "how far around from a reference angle". In this case, there is only 1 frontal, and 2 lateral dimensions, and no vertical dimension at all.
So, let's now think of a 4D planet with gravity. In the absense of anything other than time and gravity, there is 1 frontal, 1 vertical and 2 lateral dimensions. Therefore, 4D beings in such an environment would recognise "forward", "backward", "up" and "down", but would not recognise "left" and "right". They too may work in polar coodinates for the two lateral dimensions, identifying a point in 4D space as "this far forward, this far up, this far out and this far around from a reference angle".
However, 4D beings may have reasons to design structures that identify dimensions as separate again. For example, my
planar rail system creates an environment where all four dimensions have their own special properties, separating the 2 lateral dimensions into a "confined lateral" and a "navigable lateral". Thus one may use "left" and "right" to describe the navigable lateral, while using "ana" and "kata" to describe the confined lateral, or vice versa.