If you are using a VPN, then sort of. It depends on the details. They need to at least be a no-log VPN for it to be remotely true, and even then, fingerprinting a user isn’t that difficult. Though for most, DDG is only a search engine, and a search engine definitely isn’t hiding squat on its own.
Isn’t the very article about economists taking a closer look at the general sex worker index more than merely saying someone called it?