When waves overlap on a guitar string they are two different waves whose state covers the same area. A wave superposition in an atom is a single wave that has a position state that's more complex than being in a single location.
Superposition is the mathematical description of _our_ uncertainty about position of a particle.
The physical wave in a guitar string does redistribution of mass in the string using energy. The physical wave does some work, while superposition does nothing, because superposition is used for predictions only. When we know the location or other properties of a particle after a measurement, then its superposition is meaningless.
They share nothing in common in the physical world, while they share a lot in mathematical description of their behavior.