By my understanding, this bug was never fully fixed, although some change in the SE software circa 2011 rectified the displayed usernames on most community wiki posts at that time. For instance, the list of linked questions on the Meta SE thread from which John Omielan's answer is based shows that this bug has been reported several times since 2011.
The simplest workaround that currently exists is to make any (small) edit to the community wiki post. This should update the displayed username to the one currently used by the author of that post. In the case of the answer in which you noticed this bug, perhaps the OP had updated their username only after both edits were made, instead of between the two edits; that would explain why the multiple revisions did not trigger an update to the displayed username.
Of course, the downside is that any edit bumps the thread to the front page, so it would be best to use this workaround judiciously.