I was one of the original developers on this project! It was called the Watson Assistant and was a completely different code base from the original Jeopardy code base. The dialog tree was actually fairly sophisticated in allowing for a lot of flexibility. However, I always had a concern hat developers would find it too complex to author dialogs. Apart from the dialog tree, the other components were a text classifier and an entity detection system. It has been several years since I quit IBM so I have no idea how it has evolved since then.