That is exactly what that comment implies.
Whether it is tracked explicitly or implicitly, the idea that there is a matrix that establishes your linkage to other accounts is the bit that I take issue with because the conclusion for me is that Google is able to infer things about the people they hold data on that they never ever should have access to.
If you have a credible alternative explanation of what it does mean then you are welcome to supply that but instead you are making statements that are unverifiable:
> Nothing they said implies that Google is tracking who people's partners are.
That's a very, very thin line because if Google can figure out which account to ban and which account to let live because they are close enough that without that matrix the two would be seen as the same entity then that's already many levels of privacy violation too far. Being able to derive who is partner with whom once you have that data is trivial, whether Google actually does this or not is irrelevant because you can't prove a negative.
You are well into the territory of defending the indefensible here and I'm giving you a lot of leeway because you most likely have a mortgage and a bunch of other responsibilities but effectively you are defending your employer from a claim of gathering data without consent. Which - as I probably don't need to remind you - is a massive violation of privacy.
This all revolves around implied ability, I don't give a rats ass about whether or not there is an actual implementation of that ability - as it seems you do -, Google should not have this capability because I did not consent to its tracking of the relationships of my accounts vis-a-vis other accounts. Legal basis for data processing and informed consent are both staples of privacy law.
I know that both of these, but especially consent are difficult topics for Google, they seem to approach these things from a 'we can therefore we will' angle and that has resulted time and again in them being found on the wrong side of the lines of ethics and legality. This is just one more little nail in that particular coffin.