Its the only thing I can think of, since you can find all the models on Sony`s sites, and to my knowledge there are just the 3, 1000 through 3000 with a possible new PSP this year at E3 but thats not out even in testing phases.
The ONLY thing I can think of is that its one of those knock-offs you can find around, either the look-a-likes or a chinese knock-off, like the knock-offs of the Wii (Vii or something very similar)