DuckDuckGo is not immune to this either - https://dzone.com/articles/duckduckgo-has-a-privacy-problem
These strike me as two entirely separate things that people mix up a lot...
1 - Do I want future users of this device to know what I did online? Use Private Browsing to block.
2 - Do I want Google to know what I did online? Use Duck Duck Go to block.
DDG will fix #2. It will not fix #1.
Private Browsing will fix #1. It will not fix #2.
Using both together will satisfy both, but they're often totally independent/unrelated issues.
That article is 100% complaining about how Duck Duck Go doesn't take care of #1, but I don't care about #1 most of the time - it's only #2 that I want to have handled 99% of the time.