It's a joke. A quantum leap is what you say, but a quantum in physics is all about being the smallest discrete unit of some physical property such as energy.
No, a quantum leap is any abrupt leap between any two energy levels (i.e. you can span multiple), it characterizes the abruptness, not the size.
IIRC the term's usage in English derives both from the fact that it is an abrupt leap, and also from the radical change to physics brought forth by quantum mechanics.