Noting that if I paste a URL into my WordPress.com visual editor, behind the scenes it can look up the link, pull a page title back, and create a link using the title as link text and the link set to the URL I pasted in:
I’m not sure if this requires any particular metadata on the page referenced by the link? Certainly, it doesn’t seem to work for every URL? But then, Pete Warden’s blog – what do you expect?!;-)
Will Compression Be Machine Learning’s Killer App?
Here’s a closer look, watching the page traffic that’s returned using browser developer tools (View->Developer in Chrome):
This is what’s returned:
{"success":true,"data":{"body":"<a href="https:\/\/petewarden.com\/2018\/10\/16\/will-compression-be-machine-learnings-killer-app\/">Will Compression Be Machine Learning’s Killer App?","attr":{"width":676,"height":1000}}}
And this is what was sent:
I wonder if the same mechanic is used to embed Youtube videos when you paste in a Youtube URL? Although that may be done in the web page itself (you can generate the Youtube embed code simply by extracting the video ID from the pasted URL and constructing the embed code using a template.)
OUseful.Info, the blog... 
I think this only works on WP.com I do not get the same on self hosted. My hunch is it uses the image / data found in opengraph tags in header. You see the same embedding in Slack, discourse.
@Alan Yep, I should have qualified “wordpress.com” editor. Will poke around a bit more if I make time to do so on this… (lots of other irons in other fires atm…)