Google also returns the article with this query

That depends, considering search results are usually tailored to suit individuals (if logged in).

True, but it could not return this article for anybody if it was not indexed.

Although it is fair to assume that Tim's blog post and all these new links pointing to the old article have triggered it's reindexation.

It feels a bit like quantum physics, now that the article is out, the state of the web has been observed and has changed.

DDG uses Bing as the backend.

I don't believe that's true, at least not in the way you seem to imply. It is true that Yahoo and Bing are literally the same search engine on the backend, but that is not true of DuckDuckGo and Bing.

To quote the first line of the DDG wikipedia article on how it works[0]:

> DuckDuckGo's results are a compilation of "over 400" sources, including Yahoo! Search BOSS; Wikipedia; Wolfram Alpha; Bing; its own Web crawler (the DuckDuckBot); and others.

[0] - https://en.wikipedia.org/wiki/DuckDuckGo#Overview