The raising of the head is to help swallowing. I don't know about Crested's inparticular, I have two but am not trained on rehabbing them..... but the water dragons and the iguanas that I work with will do this. Most reptile have a "gullet" or pouch that they can store food in until they are able to actually swallow it. The tounge most often does not go to the back of the throat and is no aid in swallowing like ours is. That is what causes the need to raise their heads and let the food slide down.
My cresteds will do this as well and like I said, I am just relating it to my experience in rehabbing other reptile species.