Apparently Levi's banquet for Jesus was on the day that the disciples of John the Baptist, and the Pharisees, thought should be given to fasting. "And they said to Him, 'The disciples of John often fast and offer prayers; the disciples of the Pharisees also do the same; but Yours eat and drink.'" Notice that the question. refers to Jesus' disciples, not to Jesus Himself. "This is again (v. 30) that reluctance to attack Jesus in person although the matter involves him primarily." - Lenski

The disciples of John and of the Pharisees wanted to know why the disciples of Jesus did not fast as frequently as they did. Why were the disciples of John fasting? There could be two answers: (1). Herod recently killed John and they were mourning for him; (2). Like the Pharisees, John may have encouraged his disciples to fast as an expression of mourning for sin.