Try changing the default in Safari, on the theory that it might use that as some sort of “system search engine”? Failing that, it’s probably just hardcoded.
Changed and it's still Google. Yeah the search string is probably hardcoded :(
Definitely uses Safari + Duck Duck Go for me. It appears that it just "types" the string into Safari's search bar, so whatever that does is what it does.
Try Alfred. It’s even easier. I have a global shortcut that opens a search engine prompt. Press enter to begin the search.