Allah's Favourite Author?

S 31:12-19 And we gave Luqman wisdom: Be grateful to Lah. And he who is grateful, he is only grateful for himself. And he who was ungrateful, Allah is rich, praiseworthy. 13 And when Luqman said to his son while he was exhorting him: My son, do not associate with Allah. Shirk is a great wrong. 14 And we advised man for his parents. His mother carried him in weakness upon weakness and his weaning is in two years: Be grateful to me and to your parents. To me is the destiny. 15 And if they have waged jihad on you to make you associate with me what you have no knowledge of, then do not obey them. And accompany them in the dunya decently and follow a way of him who has turned to me. Then to me is your return then I shall inform you of what you used to do. 16 My son, it, if it be the weight of a grain of mustard and it be in a rock or in the skies or on the Earth, Allah brings it. Allah is nice, an expert. 17 My son, perform salat and command kindness and forbid baseness and be patient over what has hit you. That is of the determination of affairs. 18 And do not turn your cheek to people and do not walk in the land gleefully. Allah does not love every self-conceited, proud man. 19 And be just in your walk and lower your voice. The most hideous of voices is the voice of donkeys.

How much of this is supposed to be Luqman's words? If verse 19 is his, does Allah agree regarding the donkey's voice? Is the rest his? Are verses 14 and 15 Luqman's words? If the Quran is inimitable, are Luqman's words too?