And that is your subjective interpretation.
I guess what Xanth wants to say (correctly) is that in the Astral we do not have physical timespace coordinates as such. It is (probably) a more digital/holographic reality with by far different 'laws' and rulesets that maybe we still cannot quite fathom. This physical reality is digital/holographic too, but with stricter rulesets. Hence we have 'reliable' ups and downs, lows and highs, lefts and rights, and so forth.
Of course, that does not mean that we can't use these terms metaphorically when we talk about the Astral. Low and High are correct terms when used this way. And they are helpful. It's a language thing. They are 'established' metaphors used in almost every description of non-physical reality, be it Eastern, Shamanic, even R. Monroe counted his Focus Levels from 'down' to 'up high' (C1 = physical to F27 and far beyond that).
Most of the best teachers and authors on AP (Buhlman, Bruce, Leland, Monroe etc.) use or used a similar kind of terminology including "low"/"high" and describe their experiences this way. Robert Bruce even sees the different realities as flat planes where he navigates in-between to switch them. All descriptions and experiences are correct. They are certainly not meant by most who use them to be literally interpreted in physical terms (means: the ruleset of this reality).
It's also pragmatism: Metaphors are effective elements of language by which we communicate with effectively, so we know what we are talking about and that it could be, at least approximately, the 'same thing'. Just look at David's site (http://www.inspirationstore.com/Astral-Show
), he also names one video the "Low Astral" and we know what to expect in the video beforehand. We know it's about 'evil' beings perhaps, stuck people to be retrieved, dreamers confused, some darker realms or neighbourhoods, perhaps our own dreamscape, etc.. We know it from our pre-knowledge what it could be about, which is also based on a linguistic convention of "low" in the context of AP beforehand without ever having started the video.
Moreover, many projectors also fly upwards into 'better' zones/planes and fly downwards into more hellish zones. I've did that too. That's just one way it often "works". I believe this is where human metaphor actually co-creates reality for the individual, so it is reversed causality somehow. Human mind created or co-created these 'realms' (most fo them I suspect) and hence our rules and understanding are 'programmed' into it. This applies also to the "higher" and more steady (consensus environment) realms.
Of course, this mode of transportation is subjective, too. Some people only "beam" or "jump" or "switch" or "phase" from one point to the other, hence for them down/up does not exist the same way when they move between realities / planes, etc. That is how they experience it and it is correct, too.
Still one could argue, within the reality where they are they also have coordinates of up and down (usually) - even in unstable 'lower astral' environments, and at least if it is a more "humanized" zone and not something purely energetic and 'without taking a form' - which we find most often in some of the "higher"