It was just named that "for the sake of it, it seemed a useful term" for such a gun since "who can argue with 'reason'?"
It was made by him and for him, merely as his personal example of how interestingly personalized 3D printing allows metal weapons to be. (Solid Concepts, now owned by a bigger, and publicly held, 3D printing interest Stratasys, is trying to avoid being too connected with the weapons field these days.)
The weapon was made mostly out of stainless steel with store-bought grips, using an EOS M280 3D printer. It chambers 10mm ammo and features the word "Reason" printed in the slide, and the preamble to the Declaration of Independence on the front of the grip.