Hi Paul, he most likely uses a special add-on package for Kitchen Designs. I used to do modular casework (very similar to kitchen cabinets) at a few companies and we always used add-ons for AutoCAD to do this. Yes you can do it by hand but that can be VERY time consuming.
Microvellum makes one - https://www.microvellum.com/kitchen-cabinet-software-for-autocad-users/
Here's a video of someone doing it just in AutoCAD
Good luck