Ultimately, Palpatine has to be behind the clone order, whether acting through Dooku or not. So Obi-Wan has to be unable to connect the clones to Palpatine (or anyone else) but needs to be intrigued enough to follow Jango to Geonosis to investigate. The name of Sifo Dyas, a former Jedi Council member, who is now dead, provides the lack of connection, the unknown "Tyranus" provides the intrigue.

Using the name of Qui-Gon, as Commander Courage suggested, provides both, without making reference to a character who is otherwise absent from the movies. It also provides Obi-Wan with a more personal motivation to get to the bottom of the mystery.