Wait, which translation is more accurate? This changes a lot if this is the correct one
"Yeah, they did IT. However, the author left JUST enough ambiguity (and wiggle room) in there for them to backpedal if they wanted. I mean, TECHNICALLY they could say that 'IT' was going to a hot springs again and they wouldn't be wrong. Ambiguous trolling at it's finest, LMAO."
It's up to reader/translator interpretation.
It didn't make sense to me.
Remember how she was supposed to wear a swimsuit in the hot spring, but the swimsuit broke?
I think she wants to buy new underwear so she doesn't get naked again.
She wasn't thinking about getting naked in front of him because she gets super flustered by the idea of buying underwear for his sake.
Whatever makes sense to you is fine.