https://www.bg-wiki.com/ffxi/BGWiki:Copyrights
Ownership is already taken from the authors. When you submit content to the wiki, it becomes governed under the license of the wiki. You agree to this. The license allows anyone to copy, distribute, and transmit the work as long as it is not for commercial purposes and you follow any attribution the author requests. Since there was no explicit request or license provided on his guide, the most it can be fairly read as is that you cannot take away his name and credit when copying it.
It may 'feel' wrong to you that it's no longer under his ownership/control, but legally he ceded that ownership and control with very few stipulations the second he posted it on the wiki. What he's doing now is effectively vandalism, though of course the wiki owners have a right to exercise their discretion and let him get away with it. If you don't like the idea of losing control of your own content, you should be wary of the licenses under which you're posting that content.
Edit: Just to be clear, he also cannot go back and add a license now. Old licenses are still valid for old copies of the work, even if he were to release a new identical copy with a more restrictive license.