Your link doesn't work - Is it definitely a page or is it a group? If its a group FB recently changed their settings which is causing all sort of problems like this, basically the groups are opt out now not opt in so if someone invites someone they automatically are joined and get a shed load of updates until they change teh group settings or leave - Only good thing is once they have left no one can add them again. Oh and any member can invite people not just teh admin
See some info on this here here
http://arstechnica.com/web<WBR>/news/2010/10/how-to-use-a<WBR>buse-and-leave-facebook-gr<WBR>oups.ars
If it isn't a group could it be someone else inviting them to the page? Anyone can do that not just the owner