Wow, looks like they just updated that page and removed all references to their external indexes. Very shady stuff, Kagi. I'd go as far as to say they are now lying by omission.
Our data includes anonymized API calls to traditional search indexes like Google, Mojeek and Yandex, specialized search engines like Marginalia, and sources of vertical information like Apple, Wikipedia, Open Meteo, and other APIs.
Kagi's indexes provide unique results that help you discover non-commercial websites and "small web" discussions surrounding a particular topic.
I wouldn't even care that Google is their main index, that's fine and they can't be expected to compete with the billions of dollars Google spends on indexing. But the lack of transparency and shady business practices are a big turn-off for me.