After looking at the user's profile and the link in the end, I flagged it as spam. I also posted a comment asking the user to state any affiliation to the site. In reply to that comment, he said that he was not affiliated with the site. Since his profile description and his statement contradicted each other, it attracted more flags.
He later deleted his post. And I got the flag declined notice with the following message:
declined - a moderator reviewed your flag, but found no evidence to support it
This declined reason is ambiguous. I guess the evidence is all there in the revision history. Though I don't have any issue with the declined flag, I would like to get clarification about it. Thanks.