Fox News is still insisting he was decapitated. No source on that detail though.
And yes, decapitation is the head. Limbs get severed, your head gets decapitated.
Not to be too grisly in the details, but often when someone is decapitated, their head isn't actually removed from their body. People often suffer what's known as 'internal decapitation'. This is when your head stays on firm, but the inner workings are detached inside the neck, causing the same result even though you stay in one piece.
(Spent too many years as a criminal prosecutor!