To give another deviant a direct link to this FAQ answer, use the following code in your comment or forum post:
What does it mean if I receive or see a comment from "Nobody"?
If there is a lot of activity on deviantART, and one of the servers has fallen behind, this can result in comments from Nobody, with dates such as 1970 or 1969 and basically means that even though the server you are currently using does know that there is a comment for you, it does not yet know who it's from, or when it was submitted.
In case this happens to you, the best thing to do is wait and don't worry - eventually the server will catch up, and you'll see your comment just fine. You can keep on commenting too - even if your comment doesn't show up immediately, if you did not receive an error message, the comment has been stored and will show up for everyone as soon as all servers have caught up with one another.