They explain a bit more about what that means here: https://kagifeedback.org/d/2808-reconsider-your-partnership-with-brave/75

TL;DR They use multiple sources for search results besides their own indexer, the most obvious one is Google. To lessen dependence on one single search provider they have been adding other sources, one of them is now Brave. That is the whole thing.

On Dec 26, Kagi started including search results from Brave search index, after we previously added Mojeek and Yandex earlier in the year. Brave has a public search api and we currently implemented it for about 10% of queries as a first test (same as any other API we use, there is no mutual development or anything of the sorts). This was announced in our Dec 28 public changelog. Approximately a week later on Jan 5 after several posts on social media about ‘Brave partnership’ the situation escalated.]

So, if you do not like to use Google in the first place, I don’t really understand why lessening the dependence on google would be a bad thing?