Since the owner of this answer has been unobtrusive for the past three years, I would not suspect him for spamming. Nevertheless, six identical spammy answers have been posted within minutes. Should this be flagged as spam though, since this might lead to bad consequences for the user?
Just flag one of the posts as 'other' and explain what's going on. There's also a very good chance that the system has raised some additional flags to alert the moderators of duplicate content, quality, etc. Your flag on top of these adds even more validation and context, and the mods can jump in quickly.
Spam generally enjoys an extremely short life on Stack Overflow, the posts will likely be spam flagged into deletion possibly before the moderators even see the flags. If that's the case, then they have context from you right there in their dashboard to explain the 'carnage'.
You can post here if you really think more eyes are needed immediately, but be aware that this will cause quite a few people to take a sudden and potentially destructive interest in a specific user - so do so with care. In most cases, a descriptive flag is all you really need to do.
I would custom flag one of his posts explaining exactly what's wrong. A moderator has the tools to handle it.
Alternatively, a post here on meta works too.