In the OT Christ did not walk on earth as an Incarnate, but rather as a theophany. There is a difference.
Yes, there is a difference, and the difference is that theophany is Logos' manifestation without humanity. Was Melchizedek, not human?
An example of theophany is mentioned in Isa 9:6 (Septuagint)
For a child is born to us, and a son is given to us, whose government is upon his shoulder: and his name is called the Messenger1 of great counsel: for I will bring peace upon the princes, and health to him
1Greek : αγγελοσ (aggelos), angel