If I'm not mistaken, this is both Twitter syntax and terminology, i.e
@replies. It seems that this user is trying to use comments feature as if it were a Twitter timeline. It's a brand new user who probably doesn't know how to use SO yet, but is familiar with Twitter interface. Then he saw a familiar syntax for replies and also tried to do that hash-tag thing, whatever the intention was.
It is definitely abuse of comments system. The only thing I'm not sure at the moment is if it was intentional or not.
I can't see a substantial difference between this case and a case when asker adds a reply with something like I edited my answer to clarify to attract attention other than the fact that this one is far less subtle.
I remember seeing a meta post where someone was complaining about a user who kept constantly deleting and reposting the same comment in order to make the little red icon in the Stack Exchange menu appear and practically kept extorting an answer by being boring. Now that is a serious abuse of the system.