The terminology is correct. "Ambidextrous" means that the mouse can be used by right and left-handers alike, without saying anything about side buttons. "Symmetrical" describes a mouse that is axis-symmetrical, i.e., one which has side buttons on either side. A symmetrical mouse could also be called "fully ambidextrous", as a left-handed user could also use side buttons.
I'm aware these terms are often used the other way around, but if we're strictly looking at the semantics of each term, the definition above is the only correct one. The MVP Wireless is *not* symmetrical (it doesn't have side buttons on the right side, too), but it is most definitely ambidextrous; that is, it can be used with either hand.