I think Kishi wanted to 'shock' the readers by making them think it was Naruto's hand. Then you turn the page and you find it was Hinata's before the famous bitchslap.
(He used that trick a lot. Like recently with Neji's death scene. Hinata jumps in front of Naruto, you see bloodspatters, it turns out to be Neji that got stabbed instead)