Oh wow this is interesting / something to remember for my own life. So basically, they might try something out first in [small country] and if it works go to [medium country] and then if it stills works roll out to everyone?

This has been how companies have worked since forever.

In the 19th- and mid-20th centuries, all of the big advertising agencies handling consumer goods were headquartered in Chicago (many still are).

They would test products by introducing them a couple of hundred miles away in Peoria, Illinois. If the items were well accepted there, then they were rolled out to the rest of the country. It's where the expression, "But will it play in Peoria?" comes from.

This still happens. Back when Starbucks was still cool, it would roll out new drinks in Chicago and a couple of other cities as test markets, and then later in the rest of the nation if they were successful.

This makes complete sense - I just had never thought about it - Obviously, had thought about testing things in a smaller market, but for some reason my brain hadn't mapped that to software / websites / etc.

And props for history less on "But will it play in Peoria?"

New Zealand gets almost everything first. It's the ideal test market for FB to trial new features that mimic's it's primary revenue generating users in the USA and EMEA.

Yes, Google will iterate on the search results / new search result features in smaller markets also.