Interesting article and the motion does seem analogous to what is happening with the top hand when Djokovic, Safin, Nadal, Nalbandian and Gulbis hit their 2hbhs.
The top hand arm should be basically straight at contact and the bottom hand arm should adjust to allow the top hand arm to be dominant at contact. The arm moves from semi-bent (not as much as with the golf swing, but then the golf swing is much bigger) and then straighten during the pivot and swing.
The big difference between this and the fh is that the fh has the straightening taking place at the end of the backswing and with a more outward and downward pressing motion (the 'ptd') and then sort of locks into a preferred position. The 2hbh top hand arm is changing and straightening more during the forward motion.