Audio in the background does pause for a variety of reasons. But audio does not autoplay in Safari without user intervention. If your ad is auto playing, it is muted.
On Reddit as you need your finger to scroll and a lot of videos are in the way it's almost impossible to scroll without touching one-> the music will stop.
I’m not saying sound management doesn’t suck on iOS. It does. But the scenario you describe is forbidden by Safari and Chrome on mobile and desktop. Unless I’m misunderstanding something.