Hadith no: 34 Imam Malik's Muwatta, chapter on Burial, Book 16 Narrated / Authority of: Yahya related to me from Malik that he had heard that AIi ibn Abi Talib used to rest his head on graves and lie on them. Malik said, "As far as we can see ,it is only forbidden to sit on graves to relieve oneself." It would appear now that anything even remotely related to a grave becomes cannon fodder for the khawarij.
hmmm to me it seems the camera angle makes it look like a sajdah, he's sitting at an angle not flat on the floor