It's just a bit more complicated than that:

When people search, we believe they’re really looking for answers, as opposed to just links. For many categories of searches (restaurants, lyrics, weather, etc.), there is usually a specialized search engine (e.g., Tripadvisor), content site (e.g., Musixmatch), or dedicated source (e.g., Dark Sky) that does a better job of actually answering searches than a general search engine can with just links. Our long-term goal is to get you Instant Answers from these best 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.

Partners and Privacy: As per our strict privacy policy, we never share any personal information with any of our partners that could lead to the creation of search histories. When we send a request to a partner for information used in search results, the transfer of information is proxied through our servers so it stays anonymous. That means our partners see those requests as though they came from us instead of our users, and no unique identifiers are passed in that process (e.g., your IP address). That way, we can work with partners to produce relevant search result pages, while keeping you anonymous to them (and us!).

So they use some in-house tools and they source other results "largely" from Bing.

In other words: