I imagine since the dude knew he needed Meracydian Dragons for Bahamut, that he knew who he needed for another Odin. Remember that Odin is not unique to the Shroud. There is also Raiden in Eureka, which is exactly the same type of primal, just with a different blade.

Wouldn't put it past Fandango to make a similar blade, and then wrangle a dark rider for it. Guy's already going all Merlock on Garlemald. Surely he can make a little knife what turns ya into a primal.

Of course, the meta answer is because the Lunar Primals are optional super bosses in FFIV After Years, and are literally just palette swapped versions of the previous Eidolon fights.