Currently the stream.stopVideo() function can only stop the current users video. However, you do have control over who’s video is rendered with the stream.stopRenderVideo() function.
You could use Command Channel to build a system to for the host to stop a participants video, for example:
Host triggers Command Channel event to the participant client → the participant client receives the “stop video” command, → then in your code you call the stream.stopVideo() function for that participant.