You realize that Yahoo is Bing right? Yahoo outsourced its native search engine to Microsoft a while ago and has served up results from them ever since.
did you actually think that ddg runs its own crawlers, indexing, ranking, etc.?
apparently it does, in addition to other sources (https://dukgo.com/help/en_US/results/sources). But you are right about Bing being one of them. Though I wouldn't go so far as to say that duckduckgo is Bing like the gp said.
For most search queries, the results are identical or very similar, although DDG does a lot of enhancement/cleanup.