> DuckDuckGo's results are a compilation of "over 400" sources,[45] including Yahoo! Search BOSS, Wolfram Alpha, Bing, Yandex, its own web crawler (the DuckDuckBot) and others
That refers to their Instant Answers. The regular link results ("organic results") are proxied from Bing. You can compare them side by side; the order of the results may vary slightly because Bing varies things a little, but the links are the same.
The DuckDuckBot scrapes data from select websites for some Instant Answers and it grabs favicons for other sites.
HN discussion: https://news.ycombinator.com/item?id=26429942
Million Short and DDG both proxy Bing results. YaCy result quality tends to be unusable, but YaCy can be useful for intranet searches.