"On most aircraft passengers sitting over the wing have no impact on the balance of the aircraft. I suspect you were asked to be moved for a different reason and the cabin crew just used weight and balance as an excuse"
Well that is more or less correct but it depends on the size of the a/c. If we are talking about a 20 seater a/c one pax will make a difference, however on a large wide body, moving just 1 pax is a drop in ocean