The answer in question is not considered spam for several reasons. I will be quoting from Seth's answer on the related post about what constitutes spam to analyze this.
Advertisement
Is this an advertisement? Does it read like an advertisement? Spam
usually sounds very promotional.
The original text of the answer reads:
I prefer to use virtual environments to install Ubuntu. You can use
Vagrant or Docker. Both are excellent options.
Poster's opinion - yes, but not advertisement.
Disclosure
Is there a disclosure? (i.e. "I work for this company" or "I wrote
this program")
Nope.
Relation to Linux
Is it even Linux software? (most spam we get is actually for non free
Windows software, which makes this easy)
Vagrant and Docker are both Linux software, used for creating virtual environments (aka containers). They are used professionally by many companies, especially when it comes to cloud. Consider for instance Hewlett Packard . In addition, they're both included into Ubuntu repositories:
$ LC_ALL=C apt-cache policy vagrant docker
vagrant:
Installed: (none)
Candidate: 1.8.1+dfsg-1
Version table:
1.8.1+dfsg-1 500
500 http://archive.ubuntu.com/ubuntu xenial/universe amd64 Packages
500 http://archive.ubuntu.com/ubuntu xenial/universe i386 Packages
docker:
Installed: (none)
Candidate: 1.5-1
Version table:
1.5-1 500
500 http://archive.ubuntu.com/ubuntu xenial/universe amd64 Packages
The poster's intention was that it's easier to have virtual server, but original question asked about actual physical server rather than virtual environment. Hence, this is low-quality and non-answer, but not spam.
Non-answer
Does it answer the question? Spam is often posted on questions asking
for software, but it isn't always. Someone recommending a VPN service
on a question about getting a VPN to work through a proxy is not a
real answer and most likely spam.
As mentioned above, it doesn't answer specific question , hence deserves not-an-answer. Note , that Seth said "most likely". Just because a software is mentioned, doesn't mean the post is spam.
Links
Where do the links go? If it is a legit site (github, pastebin, gist,
launchpad, etc) then it is probably fine. If it is a shortened link
(goo.gl, bit.ly, etc) then it is most likely spam. Tread carefully
here.
As high-reputation user I can see the links and they go to legitimate sites.
Trolling
Is it a bunch of nonsense, like a troll would post? This isn't exactly
spam by the pure definition, but we consider it spam here.
Nope.
Criteria according to muru
Muru's criteria are not exactly exhaustive and sufficient to qualify spam.
It does not have a disclosure.
Wrong. Many answers on the site do not disclose relation to the product yet are not considered spam. Consider for instance all the posts on What Application Indicators are available ?
It promotes software or services.
The whole question about indicators could be considered a promotion. Seth's criteria are much more detailed. Just because an answer mentions software it doesn't automatically constitute spam.
It does not answer the question.
The post in question doesn't answer the original question, and it deserves a non-answer flag. But this is not sufficient reason to label it a spam.
Conclusion
Your flag was rejected properly. Although the post deserves to be deleted, because it's low quality and non-answer, it's not spam.
