The R-Tronic is not always automatic... Basically it's fly-by-wire transmission, both are sequential. It has a single clutch, so it's not comparable to DSG.

So you control the shifting by electronic pulses, and this way it's pretty easy to have it in manual sequential or just have an automatic mode.

edit:
My guess is that moving the stick to the left is putting it in auto. In this position you can change gears by flicking up or down.
http://images.leftlanenews.com/conte...08-audi-r8.jpg