However, message boards are also communities, and posting is participating in that community. When you reply to a poster, you are, in a very real sense, actually trying to talk to said poster.
That’s not to say that you should never reply to an old thread, but that it is still a good idea to see if what you said actually contains new information or would otherwise be important enough to warrant speaking.
It does seem like, in this case, you just repeated a previous post.