 This is because when we study about Buddha in ancient books, it is clearly mentioned that Buddha had a shaven head.There is also one event mentioned in the text book where a hunter while out on a hunt encounters Gautama Buddha (prince of Lumbini) in a different attire than that a prince should had.The hunter is mentioned as giving up hunting for the day, after seeing the shaven man in the middle of the jungle, considering it to be a bad omen.