[Inception]

This isn't quite accurate. A spore needs to unite with another spore of the opposite sex to create mycelium [0]. Environmental conditions dictate when the mycelium will develop a mushroom body to start the reproduction cycle over again.

I can't speak to whether or not plastic bags completely prevents spores from falling to the ground, but I agree with lumberingjack's sentiment about using a mesh bag to increase the odds of successful propagation. Mushrooms continue to drop spores even after they are picked. Taking spore prints of harvested mushrooms is one way enthusiasts create strains of their own.

[0] - https://radicalmycology.com/educational-tools/mushrooms-101/...