Our data includes anonymized API calls to traditional search indexes like Google, Yandex, Mojeek and Brave, specialized search engines like Marginalia, and sources of vertical information like Wolfram Alpha, Apple, Wikipedia, Open Meteo, Yelp, TripAdvisor and other APIs

I don’t want to be that guy, but technically they said they are using traditional indexes like Google, not that they are in fact using Google. But I guess that is splitting hairs.
Also, maybe they just dropped Google from their indexes? And what’s more: Why does it matter if they are using Google at all, when the results are satisfying?

Knowing which indexes they are using exactly would be nice to know, though.

I don’t see how this is relevant to this at all.