In verse 4 of this chapter, the brother of Jared asks God to touch the stones with his finger. God does. The brother of Jared sees the finger as a finger of flesh and blood, and falls down from fear. The brother of Jared had specifically asked that God touch the stones with his finger, but he would not have expected to actually witness the act. God had previously appeared in a cloud. While the brother of Jared, and indeed many prophets, had used anthropomorphic terms to describe God, they may not have presumed that it would be as real as what the brother of Jared saw.
This story is told as a conversation to highlight the miracle. We note that the brother of Jared clearly did not feel that a conversation with the Lord was unexpected, it was only the vision of the finger. The story has Jehovah ask why the brother of Jared had fallen, even though it is sure that God would have known the reason.
The reason was the presence of God in a recognizable form. God was not in a cloud, he was visible in a finger, a finger that suggested that there was truly a being that was recognizable as being similar to mortal humanity.