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
The dialogue in this scene is clearly expository and it definitely reads like some kind of studio note. I’m guessing Disney assumed the audience needed the stakes explicitly spelled out
Actually watching it again some big wig Disney producer type probably just thought the scene was pointless if it didn’t have dialogue
Yeah mainstream western animation, especially back then, tends to have action, dialogue, or both going on at any time. Execs saw more than a couple seconds of just scenery, emotion and were like “fill the gap with something!”
At this point in the movie Chihiro and the audience are trying to figure out what Haku’s deal is and the silence as Haku leads her through the flowers, shown from Chihiro’s perspective is clearly meant to invite the audience to ponder about him along with her, then it cuts to Chihiro’s puzzled face to show what she’s feeling
WHY AREN’T THEY TALKING
Which in the context of the scene makes sense. They’re sneaking off to a restricted area they’re not supposed to be in while most of the denizens of the springs are asleep, of course they would be keeping quiet as to not alert anyone.