You can have a symmetrical wing. It is not as efficient as a regular wing on an airplane, but it would work. It just depends on the angle of attack of the airstream/wing. That is how planes can fly upside down, greater angle of attack.

You probably refer to Tom Speers work on wingmasts on http://tspeer.com
A wingmast gives more lift for less drag compared to a pear shape. But you have to tune the wingmast right, otherwise it is worse than the pear shape (probably so at least). I would say the pear shape is more forgiving.

I dont think there is a set definition of when a mast becomes a wing mast.