Dragons were known for collecting a hoard and being defensive for it. And what did you do? Get yourself caught by a dragon and placed within his hoard. You were barely allowed to leave his cave and that was only when he was with you and watching you at all times. At least he brought you the necessities like food and water, plus he provided enough heat throughout the nights being surprisingly gentle with you. He brought you stuff to entertain you at times and was just coming back from one of his trips with a bag having stuff for his hoard and for you. But instead of him greeting you like he normally does he drops the bag down beside you before heading over and laying down in his usual sleep corner. It seems like he had bad time on his trip.