It changed when Garrison was removed.
As a city burns there is a random chance of spawning "population" (aka refugees)
For a City State these are added directly as +1 pop to the capital
For an AI there is a 75% chance these appear as a Worker unit and a 25% chance these appear as a Settler unit (without major mods to the DLL, the AI can't handle a combat unit that can also settle)
For the human these appear as a Population unit (old-west style wagon train icon). You can use these to found a new city or, if you park them in an existing non-puppet city they will add +1 to the pop