Raspbian was renamed to "Raspberry Pi OS" on the 27th of May, 2020. That's so recent you can assume that there'll be a whole bunch of naming conflicts and/or confusion.

Renamed from "Raspbian". Perhaps the article was written before the name change?

I hope there is an official release of 64-bit version soon.

https://www.raspberrypi.org/forums/viewtopic.php?f=117&t=275...

This project seems to go back at least 2 years while Raspbian changed it's name very recently.