I hope they cache search results to further reduce the number of calls to Google. And Marginalia Search was not mentioned? Marginalia Search says they are licensing their index to Kagi. Perhaps it's counted under "Our own small-web index" which is highly misleading if true.
Most "cost saving engineering" is involved in finding cases/hueristics where we only need to use a subset of sources and omitting calls in the first place, without compromising quality. For example, we probably don't need to fire all of our sources to service a query like "youtube" or "facebook".
Marginalia data is physically consolidated into the same infra that we use for small web results in our SERP, but also among other small scale sources besides those two. That line is simply referring directly to https://kagi.com/smallweb (https://github.com/kagisearch/smallweb).