Well it's certainly possible that Steyr could have the hubs themselves, they would have had the ability. But generally they sourced running gear from Sachs. Their mopeds all used Sachs engines and gear boxes - and I know that they did get three speeds for their bicycles from Sachs too (as I have had a couple which did not have sears re-branded hubs).
I'm sure if Steyr did manufacture the hubs themselves, somebody's gotta know about it.