Beheadings are not Islamic?

Book 14, Number 2665:

Narrated Aisha, Ummul Mu'minin:
No woman of Banu Qurayzah was killed except one. She was with me, talking and laughing on her back and belly (extremely), while the Apostle of Allah (peace_be_upon_him) was killing her people with the swords. Suddenly a man called her name: Where is so-and-so?

She said: I I asked: What is the matter with you? She said: I did a new act. She said: The man took her and beheaded her. She said: I will not forget that she was laughing extremely although she knew that she would be killed.