Boost

I'm assuming it pulls from "this box" (the api that built the box..)

They tend to be the newest communities. It might be using some metric that accounts for how frequently posts and or comments are made in a certain time frame and use that to gauge engagement, which fails with new communities which have existed for a very short period and a "high" number of posts and comments relative to this time frame

The list itself is generated by lemmy itself as is, and passed to boost via the api

Curious too... there is a GET /search endpoint with a sort parameter, maybe searching in the whole feed (All listing type) with the Active sort type gives these results, but not sure...