If you read DDG TOS (1) you'll see that they save your queries and are being somewhat disengunous about doing so (half-buried half-way down the page there's this gem):

"We also save searches, but again, not in a personally identifiable way, as we do not store IP addresses or unique User agent strings. We use aggregate, non-personal search data to improve things like misspellings."

I wonder how many folks that use DDG know this is taking place (or even bothered to read that far down the TOS).

(1) https://duckduckgo.com/privacy