It's a custom extension and actually a number of custom extensions, with quite a few more planned to further enhance the product experience. All extensions work together as a single unit to compose Crunchy Bridge for Analytics, but under the covers lots of building blocks that work together.

Marco and team worked were the architects behind the Citus extension for Postgres and have quite a bit of experience building advanced Postgres extensions. Marco gave a talk at PGConf EU on all the mistakes you can make when building extensions and best practices to follow–so in short quite a bit gone into the quality of this vs. a quick one off. Even in the standup with the team today it was remarked "we haven't even been able to make it segfault yet, which we could pull off quite quickly and commonly with Citus".