Before displaying a page it searches the content and injects a referrer tag to the end of URLs that match certain things. This is done instantly.
E.g. If there’s a Binance URL on the page it’ll add something like ?ref=bravebrowser
Binance will pick up that tag and give them money for any sign ups. Brave do this for any crypto services they have affiliate accounts with.
They took over a UK company called Play.com that was big in the 2010s for cheap CD purchases.