I know you can comment on message walls and I saw that you can also edit articles without being logged in, but why does Fandom reveal your IP Address for that?
You can't comment on articles if you aren't logged in. Your IP address is only revealed if you make an edit when not logged in (after giving you a warning) as the edits need to be tied to something. It's standard MediaWiki behavior.
Does that apply to message wall messages as well? I once got a message from a logged-out user who said they were too lazy to get back into their acc, and it showed up as A Fandom User.