That answer is not spam; it is considered spam a post that links to another site without any purpose for the question, or the answer.

It's not an answer at all, as it doesn't answer to what being asked. It is rather a comment, but it doesn't make sense as comment too.

A non-sense post without any link is not spam; it is spam if it contains links that don't have any purpose, if not promoting something.

If a user keep adding the link for a library in any posted answer, saying "This library can help you." on Stack Overflow those answers would be flagged as spam. If a user just writes "Me too!" as answer, that user is not considered spammer. I don't buy the assumption that the user wrote a non-sense comment to let me check his user profile, and follow a spam link. When I see a non-sense post, I just flag it; I don't look at the user profile.

That answer should rather be a comment, but it doesn't make sense as comment too.