Your eyes did not deceive you. They do advertise two other stock variations in Shotgun News, but they don't list them on the IO website. One of those other stocks is a side-folding polymer similar to the Sturmgewehr-90. The other is the over-used M-4 stock. Neither, in my opinion, look right. The sidefolder just looks ugly and the M-4 is like a good song that gets played so much, you start to hate it. Everywhere you look, the M-4 stock is on a different gun...they come with adapters so you can put them on shotguns, AKMs, G-3s, SKSs, Mini-14s & 10/22s, and who knows what else.
Anyway, I have seen one guy on another board install an East German sidefolding wire stock on his STG-2000 and the gun looks really nice and original. After all, the original STG-942 had such a stock.