AssalamuAlaikum, In your response you say that man is prone to errors of understanding and reporting but how could those errors be actually so great as to result in a fabrication of a new belief? Do you think that they might have been influenced by something else,Christianity for instance?
Your insight will be much appreciated,
There is no limit on the gravity and significance of the errors and misunderstandings that man can commit. For instance, it is quite possible that the narration of the dream of the Prophet (pbuh), in which he saw the Messiah (pbuh) and the Dajjal together may over a period of time have been misunderstood to imply the second coming of Jesus (pbuh) and, subsequently, reported as such.
As for whether the thought may or may not have been influenced by Christian ideology, this indeed is quite possible. Nevertheless, without a sound basis, we are not in a position to make such a contention.
I hope this helps.