Although Autodesk Navisworks uses the X, Y, Z coordinate system, there is no hard-and-fast rule as to which way each of these particular axes actually “points”.
Autodesk Navisworks reads the data necessary to map which way is “up” and which way is “north” directly from the files loaded into your scene. If this is not possible, by default, Z is treated as “up” and Y is treated as “north”.
It is possible to change the “up” and “north” directions for the entire model (world orientation), and the “up” direction for the current viewpoint (viewpoint up vector).