If I were in the situation the guy described I definitely would have tried swiping down and then got confused when that didn't work. I guess I'd eventually try tapping it.

I haven't used iOS in years though, maybe if I was used to it then tapping would have been my first impulse. Do you often have to tap on the top/bottom of the screen to do things?

You aren't really tapping on the top/bottom of the screen in an arbitrary way. There's a green oval indicator that you're on a call (or a blue oval if you have map navigation as I mentioned in my sibling post to yours). You tap on that indicator. It's been that way for years now. Perhaps it's not the most intuitive, but it's not totally unintuitive and it makes a lot more sense to tap an indicator object than to try swiping randomly.

On some older phones it's just a horizontal bar at the top of the screen. But it also says "touch to return to call" on it, so that should be fairly self-explanatory. :)

Also works for maps which also adds an indicator in the status bar. Very handy.

Or any other “thing” that uses your camera/mic. You will get a clear indicator that it is being used, and touching it brings you to the app in question.