It looks like Bing is just a part of the answer: https://duckduckgo.com/duckduckgo-help-pages/results/sources

Most of our search result pages feature one or more Instant Answers. To deliver Instant Answers on specific topics, DuckDuckGo leverages many sources, including specialized sources like Sportradar and crowd-sourced sites like Wikipedia. We also maintain our own crawler (DuckDuckBot) and many indexes to support our results. Of course, we have more traditional links and images in our search results too, which we largely source from Bing. Our focus is synthesizing all these sources to create a superior search experience.