Or it could be that, when you search something, you also click through to some of the results, where FB/AdWords and other trackers are present.

Alternatively, there was a fallacy of human mind(forgot the name), where if you think of something, your brain will start focusing on the random occurrences of that things in all places. So, those ads were always there, your brain just started focusing suddenly on those as you were thinking of those things.

Note: Not affiliated with DDG.

duckduckgo don't prevent website to track you or deposit cookies etc. Once you're on a website, let's say twitter, duckduckgo does nothing.

> When you view Twitter content such as embedded Tweets, buttons, or timelines integrated into other websites using Twitter for Websites, Twitter may receive information, including the web page you visited, your IP address, browser type, operating system, and cookie information. (https://developer.x.com/en/docs/twitter-for-websites/privacy)

So, if you visit a news paper that have embedded twitter post in it, twitter might know you passed by this website.

There's also the likelyhood that the pages you landed on sent your info to their "ad partners"