This is pure liberal propaganda. Moses wrote the most of the first 5 books of the Bible (the books of the LAW). Moses was raised as a grandson of the Pharaoh of Egypt and as such likely heard both oral and was exposed to written stories. The Gilgamesh Epic only proves that the story of the Flood was well regarded by civilized societies and not just a fluke Bible story. Moses was lead by the HOLY SPIRIT to record the correct version of the FLOOD story.
Gilgamesh is a myth and Moses may be based on an earlier story about Sinuhe. Exodus just didn't happen the way it is written.