Sure we saw her topless but she was halfway submerged in water and not shown in a full body pose. Up next after this scene is another scene of note for a difference in it compared to the manga. Shortly after getting there she sees a girl standing around naked and admires her beauty.
It is very similar to object censorship we get in other shows and most people upon seeing this would probably come to the same conclusion that something must had been censored there. When Hanabi goes into the hotsprings the scene is redrawn to completly remove her towel she was holding to give us full nudity of her. However in the pv for the show released some time ago we saw her ass in it.