This is air layering propagation at work, where the mature tree or plant is cloned from a stem that is still attached to it.

Layering is a simple form of propagation which consists of bending ... but will often root with no special treatment. Air layering works in a very similar way to conventional layering, except ...

If you want to try an advanced propagation technique, Hancock says to propagate your Monstera by air layering. Air layering ...