Whether or not you intended it, your words came across as aggressive and hurtful
Note that I am not saying that others were not also aggressive in their word choice; what they said could come across rudely (text is really difficult
sometimes all the time). On top of that, this is, far and away, a hot-button issue on this Stack, and it has, at times, gotten difficult to discuss; I cannot imagine the background/history of this sort of thing has helped anybody to remain calm or seek out and assume best intentions.
Unfortunately, you stepped on an invisible landmine
We have discussed editing in system tags, and/or answers assuming system tags a lot, so much that "a lot" probably isn't giving a big enough picture of just how much it's been discussed.
The most recent major revisit of the topic is this from early March 2020:
That came to a definitive stance in late June of the same year, landing on the policy that to add a system tag (often confusingly and wrongly called "guessing", when it does not actually mean guessing) is typically wrong. Of course, Meta can always bring up individual cases, such as this one; and has done so before; in fact, at least twice.
The confusing, perhaps contradicting, Meta answers have not been addressed
However, during the time between June 2020 and September 2020, competing, incompatible answers to the following question flipped in terms of their order when sorted by score (in fact, there have been a few votes just in the past five days and I wouldn't be surprised if the answers flipped again):
What this change in the score actually means is, at least to me, unclear and has not been officially addressed in any capacity that I am aware of. I completely agree that this leads to a very confusing (if not outright contradictory) set of answers to Meta questions about similar topics; it simply hasn't been addressed (yet).
To quote a recent comment there from a Diamond Moderator:
Note to all users: Recent votes on this meta have made our actual policy unclear. Current enforcement is that the OP must clarify the system and edition explicitly. This is clearly something we need to readdress and will do so soon.
Notably we also have the following question:
This is an older question (September 2018) but it is also extremely similar to the idea of adding a system tag. Instead of being about a user adding a system tag, it is about them assuming a system tag. Thus the re-revisit of the policy that I linked to at the start is, at least to me, similar enough that it can be considered a revisiting of this (at least to some extent).
To that end, the ideas expressed there would be continued now; an answer that assumes the system can be handled by the community, receiving downvotes and delete votes if they find that they are warranted.
That said, strictly speaking, an answer to a question that should have a system tag but does not have one is simply not an answer to that question. Such answers would assume a system which the original question did not have, and thus they are not actually answering the question as it was asked but are instead answering an entirely different question. This is similar to the stance that you should avoid agnostic answers to system-less questions that need system tags.