Although I got Ehrman's initial interest on that idea, I proceeded to shoot down my own idea in flames, on the basis that the Lukan text would have had to be subject to a huge conspiracy of corruption to end up with what we have now, because there are many passages that DO associate Jesus with the Son of man.
Ehrman's next response is: It was probably (to give it in its shortest version) to show those suffering that they too did not really need to suffer if God was on their side. They too could be calm and in control.
But how does this account for Luke's idea that Jesus is the Son of man who must "suffer and die"?
For me this is a mystery indeed that I think I will simply put on hold until I hear a more developed explanation. I do not have one.