I stumped Derek?
Cool. (you're working late on a Sunday!)
Here's the save that screenshot is from (scroll a bit to the left for the unit, there's a second unit in the game somewhere).
I think this is the unit XML file
I tried to reproduce it in this game and in another game (that I had researched the trade tech, in case that is part of it) but couldn't.
From memory, I wanted a 3-move pioneer, so I edited a pioneer, adding the scout trait and removing the weak trait, changed clothing, weapon, stance and background, then saved as "Settler". Built 2 of these, and noticed it lacked the 'settle' and 'outpost' abilities, but had 'propose' and 'build (road)'. Didn't pioneers in the first game have a build road capability?
Also, the additional actions:
Note the 'recruit' option, as if it's a champion unit
I'll look for an earlier save, just after the units were created.