When checked in other test tools this page/2/ request is not showing in requests.
But only in webpagetest results.
Why ?
Do you have a link to the result? Sounds like a preload or prerender directive of some kind or maybe service workers (which some tools may not show).
I have noticed this too on WordPress sites that have in the head section. I can’t replicate it loading in developer tools in Chrome or Canary on desktop so it doesn’t seem to be firing in normal browsing use.
Just because you don’t see it in dev tools, don’t assume it’s not happening 
Dev tools (and lighthouse) focuses on one specific renderer (the one you opened dev tools to inspect). It does that on purpose so you can have a bunch of other tabs open but still be able to focus on just the activity of that one renderer.
WebPageTest reports on everything the browser does. That is why you can also see certificate revocation checks in WPT but not dev tools (they are issued by the browser process without the renderer being involved.
Chrome’s prerender logic loads the content in a hidden, separate renderer: Introducing NoState Prefetch - Chrome Developers
Nothing that happens as part of prerender will show up in dev tools (or impact the traffic shaping of dev tools connection emulation) but it WILL show up in WebPageTest.
FWIW, the same is true for HTTP/2 for example. HTTP/2 PUSH’d resources will only show up in dev tools when the renderer asks for the resource from the browser. If something is pushed that the renderer never asks for you won’t see it (and the timing for when you see it in dev tools is completely wrong).
It’s likely that there is either a prerender hint in the page itself or Chrome is automatically prerendering rel=“next” pages which is why a test result or URL will help.
Thanks for the detailed explanation Patrick. I just assumed based on seeing the prefetch data in dev tools that prerender would show there too, but in saying that I haven’t used prerender in awhile.
And Chrome/Canary on desktop is prerendering the rel=“next” tag link images and all, as checked in the server logs. So there it is!
Test site: