Embeddings are created using OpenAI's ada model. They are stored in Supabase with the vector extension, which offers a simple way to compute vector similarities. Then the associated sections are added to the prompt context.
The way it went is: we built this as part of Motif for the past month, and our users loved it. Many asked for a way to add this feature to their existing sites, so we made a standalone platform that streamlines the process, and open sourced it :)