The default orientation of the virtual camera is always antegrade. If you press the space bar (short-key) to start the fly-through and the fly-over you can see that the "Play forward" button at the bottom at the right hand side of the Gentle Colon application is pressed as well.

The second "Play" button corresponds to the retrograde fly-through and fly-over! The short-key for retrograde orientation is Ctrl-Spacebar (while pressing the Ctrl-Key hit the spacebar).