The problem with "is it rude" questions is that they are often asked by someone looking for validation -
I did this thing and I was told that I was wrong to do it - is it actually rude or not?
We are not here to judge or to settle someone's argument with someone else. This can be seen in the recent question you mentioned: Is it rude to not ask for a reason first when receiving a gift (chocolate) from a colleague?
Whether it's rude or not to me or you or anyone else is irrelevant. If the person you're talking to asserts that something bothers them or that they expected something of you, that is what matters... they expect a certain reaction. They have their own set of rules that requires such a query, so whether we tell that person "yes, it's required" or "no, that's silly" is irrelevant. For that person, it is required.
Sure, we can tell you that what they're asking is stupid or wrong but that's really not going to address your interpersonal relationship with the person. This question should be edited to really focus on what the OP is trying to achieve - not validation but how to move forward from this situation... though since the situation is over, I'm not really sure how much value that's going to give them... but, rewording the question would possibly keep it more useful to others... As such, perhaps it argues more for a single broader duplicate target we can use when someone asks us questions like this that says something like what I just did but with more detail and explanation.
What should I do when my behavior/response to a situation doesn't match up with how the other person expects me to behave/respond?
Unfortunately, this seems extremely broad... perhaps we can find a better version of it that would be useful to more people... or maybe that's OK as a general place to start for these "someone called my actions rude but I didn't see them as being such, am I right?" questions. Perhaps this would be better as a meta question used as a target for a close reason:
Your question seeks to validate your own actions or those of someone else. This sort of question is a bad fit for our site as we can not judge who is "correct". Please  your question based on the guidance supplied on our [related meta post] or see the general advice on [this duplicate question].
Questions that are about specific etiquette situations should have more definite questions. Rather than asking "is this rude", ask about the etiquette:
So, instead of Is it rude to wear a sari as a westerner to a wedding in India?, ask:
As an American attending an Indian wedding in India, what is the etiquette regarding wearing a sari as a non-Indian? [question body explains in more detail]
A lot of the questions really seem like "Am I right" questions, which are often/usually XY problems:
Is it rude to ask how much a new neighbour paid for their apartment?
Is it rude to ask how much a new neighbour paid for their apartment? My view is that it isn't, because it's information that's probably their favourite topic of conversation right now, and also in the public domain.
It ends with:
Generally speaking, is my perspective on this reasonable? If it's of any relevance, I will not be deploying any offense-taking countermeasures such as the classic "if you don't mind me asking" gambit.
What they really seem to want to know is:
I have some new neighbors who I've gotten off to a rocky start with. I'd like to change this but I'm not sure how to go about it. How can I interact with them in a way that shows that I'm interested in becoming friendly?
This is a bit broad but I think the question is currently an XY problem based on their statement:
So next time I bump into them I intend to actually make an effort. Not a huge one, but an earnest one nonetheless.
So, if they want to make an effort to be friendly, why ask this specific "is this type of question friendly" instead of asking "how can I start a good relationship with my new neighbors?"
As written, it seems that they're looking for justification for their actions so that they can assert that they're being reasonable if their neighbor reacts negatively to such a question. We can't tell them what to expect because we don't know these neighbors or what they consider rude. What a "reasonable" person might find appropriate or not is irrelevant - particularly when their question gives such a bleak outlook on their relationship with this person - so what their goals are here is unclear.
But if the question focuses on the X instead of the Y, they may actually find some better solutions.
If all they really want is to know how much their neighbor paid for their home, and it is public record, why even bother asking... just look it up on the website that hosts such information. This is a non-issue.
The "is this rude" questions will generally need editing to get rid of the "is this rude" and focus on the actual question (in the case of XY issues) or focus on whether there's any (specific) cultural etiquette in a situation. If they can not be edited, they should either be closed with a special close reason explaining how the question can be improved (or linking to meta) or as a duplicate of a canonical question that explains that whether something is rude or not is subjective in most cases and that it being not rude to one person (or most people) doesn't make it justifiable in the eyes of the person you're interacting with but that we are not here to adjudicate arguments.