Whoever did it is obviously not real sharp. If you register with wikipedia and pick a screen name, your IP address is hidden. I’m sure wikipedia could be made to release it under subpoena, but a random blogger wouldn’t be able to do anything with it.
But if you aren't careful, someone can figure it out. If you know the username, this provides some hints:
If someone makes similar changes to the same page, both anonymously and when logged in, wikiwatcher spots it.