Apparently, they have their own search index, which they say covers ~95% of queries, and if the results aren't in the index, it will then get it from Google or Bing. I'd love some more details on how this works. They probably aren't scraping the whole web. Are they just mirroring Bing and Google indexes? They seem to have their own page ranking algorithm that they're hoping to get trained.
I still wouldn't use it since it falls back to Bing or Google.
Curious why you wouldn't use bing/google even if your queries are "proxied" through Brave servers? (Assuming Brave isn't also sending your IP, etc, when they submit the query to google/bing)