Even though both of you may have separate forum accounts, if you both use the same browser and computer, then the cookies which identify each of you are both stored on your computer, and when you visit the forum, either he has already logged in, without signing out, or you signed in using his cookie.
EDIT: I just noticed that I don't see any login or sign out links at the top of the forum page, so the only way that I can think of, off the top of my head, is for you and your husband to use two separate browsers when visiting the forum.