RP, you are not at the controls if the seat is motored back by several inches. As was subsequently demonstrated by this Captain in quite a dramatic fashion.
Maybe he has very long arms, some of our pilots are very odd shapes. Maybe he had cramp in his legs and was stretching them after 6 hours in the seat? Maybe he had reached back to get his TAP's or similar out of his nav bag, we are allowed to do that. I'm sure the report will explain all.
With ref to knocking the stick in error, Airbus apparently said this does happen on occasion as mentioned on here.