No, it's not rude.
If the answer doesn't help you then you can down-vote it if you want. The tool tip states "This answer is not useful".
Personally I'd only down-vote if the answer was actively unhelpful or gave incorrect information, but as @dmckee says I'd comment first just in case there was any misunderstanding.
It depends. If the answer is wrong - then yes, down-vote it the same as you would for any answer that doesn't address the question. That's not rude, that's the system working properly.
If it doesn't answer the question because you've been misunderstood, then you could consider editing the question to make your point clearer.
Not all downvoting by the question asker is rude (not at all), but I think downvoting a helpful answer that just doesn't suit one's unclear or hidden or changing needs is rude.
So, yes, in this specific case, I think you've been rude. I suppose your comment there is no such thing "preconfigured ones" refers to you can create a custom task that verifies the following files against pre-defined ones? If so, then explain why you don't want to create such pre-defined files. You're asking how to validate things, and then reject the option to create some validation files?
And I know, voting is based on questions and answers, not on users. Still, with your 335 questions and 97 answers, I'd feel extra bad if that specific downvoted answer was mine.
I like to comment on how the proposed answer fails to improve my situation first (at least, if I think they were trying) basically because I want to encourage answers.
But, if it remains unhelpful---or especially if it is counter-productive---downvotes are in order.
Downvotes shouldn't take into account whether the question is your own or not, if you can successfully ignore the fact that you know more about the problem than you have described.
In this particular case (in which the answer is mine), it wasn't so much that the question is unclear, but the understanding of the author about a concept in the question was incorrect.
Furthermore, the answer will probably be helpful in an environment different from the one of the OP, which stays hidden from the answerer.
So, downvoting answers on own questions (and actually on all questions) should occur only if the answer is wrong or irrelevant. If it is not helping because it assumes something that wasn't mentioned in the question, a comment should be added (and the question updated) to make things clearer.
Firstly I always try to up vote all answers to a question I asked if they constrain anything of value to the question and don’t duplicate an earlier answer (provided they don’t already have more vote then what I consider them to be worth, I set the bar very low for an answer to be worth 1 vote).
Then this leaves the unhelpful/duplicate answers, I will only down vote these if:
The answerer has not read the question (and tags), e.g gives an Asp.net answer to a WPF question), I will also comment, normally the answer is deleted quickly in these cases.
The answer is clearly wrong, so it gets below answers that are just not helpful. By the time I down vote these, they normally have comment from other people on them explaining way they are wrong.
The answer is clearly a duplicate answer, (a short answer that contain the important point from a hard to understand long answer may not be a duplicate)
The answer tells me to rewrite history – (telling me to rewrite a code base that is many years old that has many programmers working on it, so as to avoid the problem I am asking about is not of value).