You could have checked this assertion by reading DDG's plain-language privacy policy:
When you access DuckDuckGo (or any Web site), your Web browser automatically sends information about your computer, e.g. your User agent and IP address.
Because this information could be used to link you to your searches, we do not log (store) it at all. This is a very unusual practice, but we feel it is an important step to protect your privacy.
Edit: TOS -> privacy policy