You're entirely correct - it's a modified differential drive.
The two shafts are coaxial to each other and drive their corresponding gears in opposite directions. The frame is fixed relative to one shaft but mobile relative to the other, which is where the extra 1/2 of relative motion comes from.
The traditional way to do this was with a crossed belt. This is the higher-friction lower-slippage version of that.
The two shafts are coaxial to each other and drive their corresponding gears in opposite directions. The frame is fixed relative to one shaft but mobile relative to the other, which is where the extra 1/2 of relative motion comes from.
The traditional way to do this was with a crossed belt. This is the higher-friction lower-slippage version of that.