Calls him Lord.
So how can he be
The large crowd
Was listening to him
αὐτὸς Δαυεὶδ λέγει αὐτὸν Κύριον, καὶ πόθεν αὐτοῦ ἐστιν υἱός; Καὶ ὁ πολὺς ὄχλος ἤκουεν αὐτοῦ ἡδέως.
There is something similar in Matthew, chapter 22:35-37, and Luke, chapter 20:45. What did David mean when he called the future Messiah Christ, a son of David? The traditional belief was that the Messiah Christ would be the son or descendent of David. Jesus then posed this big question. Mark indicated that Jesus asked how can David call the Messiah Lord (αὐτὸς Δαυεὶδ λέγει αὐτὸν Κύριον) and yet be the son of David (καὶ πόθεν αὐτοῦ ἐστιν υἱός)? This was a trick question. Why would David call his future son or descendant his own Lord or master, or consider him greater? The implication was that Jesus, the Son of Man, and descendant of David, was greater than David. Peter, in fact, repeated this citation of Psalm 110 in his preaching in the Acts of the Apostles, chapter 2:34-35, also. Only Mark had the comment that the large crowd was listening to Jesus with delight or gladly (Καὶ ὁ πολὺς ὄχλος ἤκουεν αὐτοῦ ἡδέως).