I've no experience with game dev, but in other areas of development what you need is often not known ahead of time (which I believe the parent is trying to say). Operating under those conditions makes the Position abstraction somewhat arbitrary (until it's obvious it's needed by other parts of the system). Aggressive refactoring and robust testing are necessary when operating under these conditions.
Well that's kind of the point of software engineering, isn't it? Actually typing code is only a small part of software engineering, and if you don't know what you need yet, then you're probably not ready to write code. That doesn't mean you're not being a productive software engineer! It just means you're still working toward that point.
I could be more clear about "what you need" actually means. Let's say I sit down to (A) prove the four-color theorem, which says that no more than 4 colors are needed to color in a 2D map with no two adjacent regions having the same color; (B) write a function to color a map using as few colors as possible. Before I can start on the meat of it, I have to decide exactly what I mean by "map". Anything that (A) relies on my proof or (B) calls my function is going to need to turn their data into the kind of "map" I'm working with.
Oh, I know what a map is: it's an ArcGIS Pro 10.7 Geodatabase with a Polygon layer! Hand me one of those and I'll assign a 32-bit ARGB value to each polygon. What? You don't have ArcGIS Pro 10.7? Well, sucks to be you. Obviously it has to be that, since I need insert esoteric proprietary feature in order to color it.
Hmm, well, okay, maybe I don't need every feature of ArcGIS Pro 10.7 Geodatabase Polygon layers. In fact, I really just need a list of regions and how they're connected. Do I need literally every wiggle-waggle of every border between each region? Well, not really ... in fact all I really need to know is which ones touch, and which ones don't. In fact, it turns out what I need is a Planar Graph. It probably shouldn't have any loops (nodes connected to themselves) either. A loopless planar graph. If you hand me one of those, I can color it for you -- in fact, I'll just assign each node 1 through (up to) 4 to represent the colors, and you can do whatever you want with that information, rather than me picking the actual ARGB values for you.
The reason I associated it with a math proof is because it's more clear in that case that reducing the preconditions on the objects you accept increases the power of your proof. Proving something interesting about all multiples of 5 is less powerful than proving it about all integers, and less powerful than proving it about all elements of an Abelian Group, etc. Writing your code to work on any loopless planar graph is much more powerful than writing it to only work on <Random Complex Proprietary Format>.
And we settled on "loopless planar graph" not because we had a bunch of graphs lying around -- we probably didn't! We probably actually had a map representation we've used elsewhere. We settled on "loopless planar graph" because that is the minimal possible description of the objects we can run our code on. That's what I mean by "what we need to do our job". That is the birth of an abstraction.
I've no experience with game dev, but in other areas of development what you need is often not known ahead of time (which I believe the parent is trying to say). Operating under those conditions makes the Position abstraction somewhat arbitrary (until it's obvious it's needed by other parts of the system). Aggressive refactoring and robust testing are necessary when operating under these conditions.