What is meant by the phrase in the hadith, "a journey of forty years" and "a journey of seventy years"?

Question : Forty years, what is meant?

Answer : Yes, if he says forty years, or more, or less, the meaning is the usual camel journey among them. Yes, because the Messenger (peace and blessings be upon him) addresses people with what they know. People did not know that there was an airplane flying in the air at this speed. Yes, rather, he mentions to us that a man came from a foreign land and started telling people that he had ridden in an airplane. They asked, "What is an airplane?" He said, "An airplane is metal that you ride in and it flies." They said, "Between the sky and the earth?" He said, "Between the sky and the earth." So they went to the prince and said to him, "Imprison this man; this man is insane." Yes, and this is the truth: if he had told us this, we would not have believed that metal weighing so many tons, with a scholar inside, has airplanes that carry four hundred people with their belongings. So the Messenger (peace and blessings be upon him), when he addresses and estimates, estimates by what he knows.