Thanks for explaining. However, a couple of further questions.
How do I edit the Head HTML for the document? In your example, there is an extra tab 'Head HTML', in addition to the 'pauseAllVimeoVideos' function tab. It looks from that it's possible to edit the Head HTML inside Hype, is that the case? This post on the forum suggests it is https://forums.tumult.com/t/cant-edit-head-html/10771, but I can't find where.
Secondly, in your example the sole purpose of the button is to pause the video. However, I wanted the video to pause or be silent when moving to the next scene. The button would thus have a dual purpose - to move to the next scene and to pause the video. Could I use the Timeline actions '+' button to add the pause command?