Why a close conductor does not propagate electromagnetic signal
A closed conductor as shown in the video does propagate an EM wave, just very inefficiently if the loop is small. It's not until the loop gets to be an appreciable fraction of the wavelength that the loop becomes efficient. A loop makes an excellent antenna when it's big enough.

I'm afraid the author of the video was (at best) trying to simplify to the point where he was confusing the watcher, or (at worst) didn't know what he was talking about.