Youāre right about the scaling being sort of easy. If he does so in the 3D model (vs. just with the 2D patterns), he then has to re-export & set up the new pattern files.
The tricky bit is with the slots that have to accept a fixed tab thickness of plywood or other material. Since those donāt change, the slot width has to remain constant after scaling, otherwise the fit becomes too loose or too tight.
An advantage to scaling in the 3D model is that instead of making a slot width be a hard-typed number, in some packages it can be a variable which is adjusted, instantly making all the slots the proper width after scaling.
For the re-scaling to be easy, it sounds like Mr Duck is using tricks like that.