There are a few (at least 1) on-set photos of this prop from ROTS. Apparently Obi was going to start the movie with this saber but lose it early on and replace it with the known EP3 saber but that idea was scrapped and instead he just always has the EP3 saber.
I believe those on-set photos were actually early costume/lighting/camera/whatever test photos, taken in Padme’s apartment set. There are photos of Christensen in the same set, probably taken around the same time.
I would guess that the prop department made the salt shaker saber just in case Lucas decided to transition from the TMP/AOTC style prop to the ANH style during ROTS. So, that prop, already being on hand, was used for the photo session. Of course, Kenobi ended up starting out in the film with the ANH-style saber.