Why should the outside disc brake pad be closer to the rotor than the inside one?
SRAM's brake setup instructions for BB7 brakes (select user manual from the service documents, step 10 in the user manual) specify that the inboard/fixed pad should be further from the rotor than the outboard/moving pad. The ParkTool instructions that @jimirings links in their comment are specific to this model of brake and repeat the manufacturers instructions in this regard.
Other manufacturers provide different advice, for example Tektro's instructions for their mechanical disk brakes (TRP Online Resources - select &quot;All Spyre and Spyke models&quot; from the road disc subheading under the user manuals section, Tektro Mechanical Disk Brake Owner's Manual, or Tektro Support &gt; Download - select &quot;Mechanical Disk Brake - User Guide&quot;) specify that the brake pads should be evenly spaced on both sides of the rotor. The Montague blog you've linked to use a Tektro Novella brake but repeat the instructions given by SRAM, not what Tektro recommend.
Neither manufacturer give any reason for the specific alignment, the only reference I could find was the following section from CX Magazine's article How to: Set Up &amp; Adjust Mechanical Disk Brakes:

Now look through the caliper. The rotor should be sitting center in the gap or slightly to the outboard side. This should position the inboard pad into the gap.
This inboard pad position should be one of your greatest priorities. If the inboard pad is too far out, when you hit the brake, the outboard pad will clamp the rotor against the caliper instead of the brake pad.

The pictures included make it clear that the caliper housing should be slightly offset to ensure that as the fixed inboard pad wears and the rotor flexes it does not contact the caliper housing itself. This would lead to damage to the rotor and/or the caliper.
You should probably still follow the manufacturers recommendations for your given brake model, however aligning the caliper to have more space on the fixed side then aligning the pads evenly would also be suitable if you are unable to find specific instructions from your manufacturer.