No one has a source for “DuckDuckGo is just Bing” either. We know that they use Bing, but not for what, people have just asserted that DDG is just Bing (or Yandex), but no one seems to be able to provide at source to back up the claim.
>To do that, DuckDuckGo gets its results from over four hundred sources. These include hundreds of vertical sources delivering niche Instant Answers, DuckDuckBot (our crawler) and crowd-sourced sites (like Wikipedia, stored in our answer indexes). We also of course have more traditional links in the search results, which we also source from multiple partners, though most commonly from Bing (and none from Google).[0]
Seems pretty clear their standard search results come from Bing. It even used to say "multiple partners like Bing, Yahoo, etc" but Yahoo was also powered by Bing. They like to change the wording to make themselves sound less reliant on Bing even though if Bing were to cut off access, DuckDuckGo would immediately cease working.
I’ve read that multiple times, and no, that’s not clear. At best we can read it as “Results from Bing are mixed into their search results”. Most likely a high percentage, but we don’t know.
Mission accomplished then because they don't want to make it clear. If you really care that much, go back through all the different revisions of that statement through the Internet Archive and see how many times they've been dancing around saying the exact same thing: it's just fucking Bing. Their own crawler returns results for very specific limited topics in their segregated boxes. If they had even one source for one specific query, say "purple cats" that they didn't use Bing for, they could technically claim it's only "mostly" Bing.
We can infer some things about DDG based published data on crawler and bot activity. DDG's index is pretty comparable to both Google and Bing, but their bot is no where to be found in activity stats. So it's pretty reasonable to think that at minimum their index is primarily derived from 3rd parties.
In my opinion, I don't think it should matter too much that they might not be crawling for their own index as long as they're reordering the results. But I do think there is some stigma where metasearch engines aren't looked at with as much prestige.
AFAICT, other than those information boxes that turn up on the top of searches, the actual search results are almost entirely powerer by bing, although as you said, they've always dodged the question.