Well, that may have been the original intent, and may have been the situation until the G22 came along. The G22 does not use an aftermarket stock, and there is no version of the G22 with a conventional stock, but the CFC has decided that the G22 stock is a prohibited device.
The aftermarket bullpup prohibition may have come about because of the Muzzelite 10/22 and Mini-14 stocks - these may have got tagged when the nasty looking black guns were being listed for prohibition. Incidentally, the 10/22 Muzzelite stock is a really tacky piece of equipment. Chap I knew had one years ago. We were not impressed.
A number of years ago, there was another bullpup .22 sold for a while. I can't remember its make or model, but it was advertised in The Gunrunner or in Access. It would be interesting to see if its stock has been classified as prohib. in addition to the G22's stock.