I said something along those lines a while ago..
It was made to be a plugin for vBulletin instead of a whole new mod, and as such it tricks the arcade script in to thinking that the forum software it is installed on is an Invision Board and not a vBulletin. Apparantly this was done so that any plugins or updates made for ibProArcade can be brought over to the vBulletin version easily without the author having to update 2 lots of code.