Wayners has no disc brake mounts on his frame.
The one in the link is a front brake.
BITD when discs first made an appearance,before frame makers caught up and started putting mounts on frames we had disc on the front, and V's on the rear.
Back then in them olden days, the only way to fit a rear disc was to use a Hope No2 caliper, which mounted to the frame via a mount that bolted onto the non drive dropout. A Hope hub with an axle shortened to 122mm slotted into part of that dropout mount, an XL skewer(same one used for Hope tandem rears) was used to hold the whole thing together.
Pic of my old Orange Clockwork.using that system.
After that they developed an IS mount that used the same axle/dropout attachment but allowed another caliper sizes to be fitted(The No2 caliper could only be used with a Hope 155mm rotor). Pic 2 is that system mounted to my Ti Raleigh Torus
Pretty much after that point manufacturers started fitting IS mounts onto frames. In the early days it was actually Hope mechanical cable disc calipers that pretty much started the whole shebang in the UK.
Pic 3 showing a 2nd generation Hope mechanical cable brake( from my early hope collection). That was fitted by hooking on to the front hub and clamping around the fork leg.