Navmesh is quite simply a path following technique. It can on the fly determine to change its route based on optimal settings for quickest route. Imagine a satnav, turn left, turn right, turn around when possible (shut up machine.... . lol

).
Using a navmesh is no different to create a spline path that you place manually around the objects that the character then follow except, if something blocks the path a new path is configured at that moment.
So in a sense, navmesh is a movement control helper not an AI.