Pattern refers to the machining part of the process.
From the 'blurb'...
We currently offer Pattern, Pattern Thin, and Pattern Regular neck shapes on our Core electric models. These came about through a new method we have to design, program, and cut our necks.
When I started building guitars, I carved all necks by hand. Then, when we started production, we went to a duplicarver and finally to CNC machines. With each progression, PRS neck shapes became more and more consistent, but we were still starting with a hand-carved neck which we then programmed to be duplicated. Now, our R&D department has software that we use to digitally create a neck to the exact specifications we want at every point, and from this digital rendering (the starting "pattern"), we are able to program our CNC machines to create great neck shapes. It's a new tool that helps us to get to the same end: a strong, precise, and very comfortable neck. By achieving that, we hope that when you pick up a PRS it feels like home to you.
I hope this goes some way to tell you why 'Pattern' is used to denote a PRS neck shape. Of course PRS will finish the shaping, remove any CNC machine cutting marks with sanding but the starting pattern is used to create the different neck shapes consistently and quickly too.