Fundamentally different. Autocad is a CAD software and Blender is not. CAD softwares use different modeling paradigms like nurbs and solid modeling, Blender is mainly about polygonal modeling.
When it’s about visuals, Blender is a good tool for that. When it’s about sending the model to a CAM software for toolpaths, or doing structural analysis, then that’s a job for a CAD.
Modeling paradigms in CAD tools have absolute precision, polygonal modeling is approximation of curves and surfaces (straight edges, flat polygons) and that’s why it’s inherently inaccurate. Won’t need the accuracy when it’s purely about visuals, but having that and the parametric modeling style, it results to different tools/workflows/options. A simple measurement for example could be different: with a polygonal model a measurement tool might not give the exact number, but would expect that from a CAD tool. Doesn’t matter how the numerical measurement is added in a picture, but it would matter in a workflow, especially if there’s an automatic tool to do it.
There’s also https://www.ptc.com/en/cad-software-blog/parametric-vs-direct-modeling-which-side-are-you-on
That points out good reasons why some studios use Blender in their pipeline, it speeds up the design process, and once that is done they move to CAD for surfacing and to support the engineering process. There has been couple of talks in blender conference about that, the synopsis alone tells a lot
https://www.blender.org/conference/2015/presentations/224
https://www.blender.org/conference/2016/presentations/264