That blog post is about a partnership (which ended), but you probably saw some sponsored images at the time, in new tab pages (1 of 4 then, I think; the rest are just art images).
These are non-tracking, carefully designed (including vetting by Brave), brand advertising images. They are not ads (we never did this) inserted into publisher pages, or (opt-in only) push notifications.
Brave has been working to find ways to sustain ourselves, and these sponsored images are still a good revenue line, although lesser now vs other lines. If you want, turn them off.
Free riding is always an user right, we don't try to stop it on principle, as if we ever could with open source. But there's no free lunch: if you use Firefox, you are Google's product. If you use a Firefox fork, you're free riding on Gecko which costs a lot to maintain. HTH
