An IP address like that is recorded when the user isn't signed-in. If I had to take a guess, it could be a family member who does have a WikiTree account and saw an e-mail update that included the change. When they clicked the link in their e-mail they weren't already signed-in and didn't think to do that first.
If you were really concerned, you could track down the IP. You might be able to find out the location where it's used, or at least the ISP.