There certainly are, but something like this would immediately get picked up and banned. It's hard to cheat without being blatantly obvious.

The players in quick play are absolutely not bots. Botting is the number one way to get yourself permanently banned.

The game client is built with PixiJS, and otherwise mostly uses vanilla JS. The backend is built with Node.js, and the game uses a custom WebSocket protocol called Ribbon.

In fact, there's a whole list of open source dependencies at https://tetr.io/about/acknowledgements/.

Not sure how applicable it would be to your use case, but TETR.IO uses a service called AdinPlay for monetisation.

Nope, some of the best players in the world hang out in Quick Play, and they're simply built different.