Were they?
Please point to the ones you perceive as “off-topic”.
The fact that the authors of those posts kept writing the off-topic posts clearly annoyed other forum members, otherwise they wouldn’t have flagged them.
I had the impression that some people just wanted to try how this can be used to suppress posts they do not like, and understood that they can play “secret police”, because the flagging process is absolutely opaque to other forum users.
Removing posts which violate our rules hardly counts as censorship.
Which rules do you mean?
AFAICS, the FAQ only contains high-level statements, but not rules or terms and conditions, which a post can be checked against on a rational basis.
BTW, in contrast do Discourse, professional censors usually have a large rule-set (the PRC, the “Third Reich”, etc.).
But ultimately censorship is censorship, regardless if and which rules are applied.
Side note: This was neither a nice or informed try (for a justification) from my POV.
Please use honest and clear terms: These posts are not “hidden”, they are eradicated, i.e. censored.
They are undone, as if they never have been there.
This is exactly what censoring is about: To let statements and opinions vanish, as if they never existed.
Those hidden posts were not about that topic.
I do not concur: AFAIR remember they were still loosely related to the original topic, i.e. triggered by it.
But we cannot discuss this, because they are censored, hence the base of any argument (both yours and mine) has been erased.
You are free to repeat those posts in threads which are relevant to them.
Pun intended?
You suggest to “repeat eradicated posts”, most of which were not mine? Sorry, this is not funny at all IMO. 
Or is that statement of yours just meant as a “power game”?
BTW, if ones rereads the thread that triggered this discussion (“Totally Buggy OS …”) in its current state, large parts of it have become senseless garble now, because most messages have been censored. IMO this does not provide a positive outlook on the future of this forum, if this result is what you perceive and define as “proper handling of flaggings”.