Yes, it is correct. It means that there are two different protocols used by ZIP drives for their parallel interface. The old protocol works with the DX2 and the new one doesn't.
If you buy a new ZIP drive it's guaranteed not to work with the DX2.
> And about the Diskdual: I have an old IDE 4X CDROM drive, will it work with the diskdual?
Most likely it will. I think pretty much any IDE CD-ROM drive will.