This video that was posted here yesterday shows some details: https://youtu.be/W420BOqga_s?t=93

Apparently there is scraping of public data + keyword matching + moderators filtering the matches.

An example that he shows a bit earlier in the video comes from this page, which has an RSS feed: https://www.cityofsanbenito.com/AgendaCenter/City-Commission...

The video says it's open source but I can't find the source.