During this time, I believe, "Son of God" was more of a reference to a very righteous man (think in the Stoic sense of a Sapien), and not a literal son of God as in a demi-god. I can't see the later sense having played well with Judaism's weird concept of Monotheism.
In my studying of the Iudean texts, the term son of man seemed to be a term that generally referred to the human race or to a mortal being. However, there is an old book known as the Book of Enoch (claimed to be written by some ancient holy man of sorts) where the term is used of a figure who would one day
be worshipped as a god and mete out judgment against the nations or something along those lines. Maybe this Jesus was trying to identify himself with this particular character.