不解 Do you know what mean that the boy said?

不解 Do you know what mean that the boy said?
A clever boy
This story happened in a small town near London. In this small town there lived an old woman.Her son worked in London.
One day,the old woman wanted to go to London to see her son.She got up early and reached the small station at nine o'clock in the morning.Because this was her first trip to london,she didn't know the train time.She was very worried.
Just at that moment,she saw a little boy running towards her. She stopped him and asked him what time the train would arrive and when the train would leave for London.
The little boy looked at the woman,and said [ tu: tu: tu: tu: tu: tu:], Then he ran away.
The old woman was very surprised and got very angry. She thought and thought. At last,she began to smile,shouting,"What a clever boy! He had told me the train time in such a way."
Five hours later,after she got on the train she was still thinking of the clever boy.

Do you know what mean that the boy said?