@Yannick I figured out how to capture what looks like another tentacle of the same issue. Look at this what happens when I have a YouTube vid in full screen, pause it, then switch to another app; it self-unpauses:
If the YouTube vid is not in full screen, the problem doesn't seem to happen:
I have checked and confirmed, this auto-unpause behaviour does not occur in Safari, even when the YouTube vid is in full screen mode.