They mention this in the article. But to sum up, each connection in PG is handled by its own OS process. Postgres behind the scenes is composed by multiple single-threaded applications.
This comes with the advantes for Pg developers (and us!) that they don't need to deal with tons of data races issues, but the trade off is that memory wise, a process takes way more memory than a thread.
This comes with the advantes for Pg developers (and us!) that they don't need to deal with tons of data races issues, but the trade off is that memory wise, a process takes way more memory than a thread.