All the doofy dipshits who claimed that no sir, no way was Microsoft gleaning data from your computer, should read the above.
The only reason search would break this way is if Microsoft was recording and sending along your every local search term to somewhere outside of your machine. There is simply no other way this particular problem could happen.
Search has never, ever worked correctly in Windows (or on the Mac, for that matter), but on Windows it’s now a whole new level of appalling and user-hostile. The most shocking thing about Windows 10 search is that it often cannot find default installed apps on a brand new machine with no installs, changes, or modifications.
How, just how, can you fail that hard?