It's from the Windows 98 Plus Pack. They didn't rewrite it for Windows 2000, they just used it as-is, so it retains the Windows 98 "Plus" look.
Oh that old chestnut. Is 2000 filled with 98 and 95 UIs like modern times?
Yes, but 95+98+2000 were basically all of the same design philosophy, so it doesn't stick out like a sore thumb when something was not changed from 95.
Except for the folder chooser from Win 3.1 that still lingers around in Win 11.