I think it's important to distinguish between downwind sailing and sailing before the wind, which is straight downwind, and cannot possibly go faster than the wind (you'd have a perpetuum mobile if you could do that).
From what I understand, faster-than-the-wind downwind sailing involves tacking between broad reaches, where the wind still comes in at an angle.
Even more astonishingly are the remote controlled sail planes than not only exceed the speed of the wind, their performance is limited by the sound barrier. "Dynamic soaring" https://newatlas.com/aircraft/dynamic-soaring-speed-record-s...