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
With Spirited Away, it’s important not to get dubtitles, which is what you did
I legit didn’t even know those were a thing! I mean yes, I’ve played games in English with the Japanese audio track and noticed some pretty large differences between the localised English script and the Japanese script but I didn’t realise anime dubs went as far as to add entirely new lines.
Lesson learned though, I went and grabbed another set of subs based on the Japanese version which made the experience of watching the movie far less distracting