I'm rewatching Spirited Away with English subs I grabbed off opensubtitles.org and I had already been confused by some phantom lines that didn't correspond to any spoken dialogue but this scene made it obvious what was happening- there's extra lines added in places where the characters are facing away from the camera 
Either the subtitler was hallucinating or these originate from the dub. I grew up watching a VHS tape 
in Japanese with Finnish subtitles and I don't recall this scene having dialogue
Huh, I've never used the Xbox Game Bar but that seems odd. Googling the problem, it seems like another possibility is that that your system volume is low (even though it's plenty loud enough for you to hear it through your speakers/headphones) which results in low signal level for the recording; I know personally that if I plugged my headphones into my PC directly I would only raise the system volume to about 4-6%. You could try maxxing out both the system volume and the player volume (if applicable) but with your headphones/speakers off and see if that improves things.
Clip's still pretty damn quiet, but if I max the volume out on my phone (~4x higher than I'd usually have it) I can hear it okay.
My system volume is already maxed out since I have a volume knob on my headphones that I use to control volume instead