Builder captured in unfinished district

[Minou]

Just noticed this for the first time and was wondering if it was a change made in the August update or just something I never noticed before. I captured a Mali city and there was a Builder hanging around outside the city. When I took the city, the game announced I had captured a unit and the Builder shifted to my control. I have captured Builders that were in the City Center (or Encampment), but never one that was just in the territory that swapped. The Builder seems to have been standing on an unfinished district. I wonder if this was what caused the capture?

Has anyone else experience this? I am wondering if it also affects Settlers?