Some of the wrong ones were from longtime users who ought to know by now what the different flags mean.
I'm (definitely) not a long-time user, but I feel that the current explanations are slightly (just slightly; no more no less) mismatched with the actual descriptions:
The Very Low Quality Flag is officially defined for (reworded for your reading experience):
- Severe formatting issues. The post is not worth salvaging and should be deleted. Like, right when it was posted, and only the original posted him(her)self can salvage the post after hours of hard work. Okay I exaggerate, but such severity of formatting issues does exist:
- Caps mixed in with horrible use of spacing, fragments of words harming readability, code blocks and blockquotes are misused of such severity that deems the post unreadable to an average user even to a reasonable tolerance.
- CHECK OUT MY CODE
var foo = new foo();
foo += foo - foo + bar + -bar * bar
- Severe content issues. For decent examples, check out Gems From Stack Exchange — Most screenshotted posts there deserves a missle wave of VLQ flags.
The Offensive Flag is officially defined for (reworded for your reading experience):
- Extreme case! Harsh destruction is needed. The content itself makes it 100% certain of a need of a nuclear blast. Cases such as:
- Hate or abusive speech.
- The post has more than severe formatting or content problems.
- Inappropriate for no matter whoever looks at it, such as NSFW pictures.
Bonus: Shog9 himself has said that "If someone is abusing the site by posting gibberish, flag it as such." This establishes a need to flag "asdf"-like content with The Offensive Flag.
Therefore, while it's true that your linked answer is not SPAM, VLQ flags and Offensive flags were correct approaches to take in this case; Not An Answer flags do not have an official FAQ post on The Meta, however according to their description:
This was posted as an answer, but it does not attempt to answer the question. It should possibly be an edit, a comment, another question, or deleted altogether.
This kind of flags are for anything that fell into the wrong box — and is a question / a need of bounty / comment / resource recommendation that should have been in a comment, not its own post / et cetera. Abusive posts should be flagged with The Offensive Flag or, at minimal, The Very Low Quality Flag.