Uh, no, it isn't. Alan released a kit a few years back. I'm pretty sure of this fact, 'cos it's in my stash. :) Alan (incorrectly) labelled it on the box as a "Bison I", which is maybe why you didn't remember it.
Of course, I expect the Dragon kit will be somewhat better ....
Alan also released the sIG 33 as a stand-alone kit.
It needs to be remembered that those "previous interior bits" are from Dragon's updated Pz.IA kits; none of Dragon's previous Pz.IB kits include any interiors. The differences are probably only minor, but anyone interested in detailing the interior needs to keep this in mind.
Bruce Melbourne, Australia