I agree that Moses was meticulous, and followed any instruction from God to a "T". I don't think though that the illustration of a non-literal snake, who was definitely Satan would break that rule. Whether by a personal revelation, or having the information passed down.
Some of the reasons I don't think the snake was literal are, the snake was part of God's creation addressed as being good. The description given of the snake was of an evil nature. It seems the earliest versions of the bible referred to the snake as separate from any beast of the field which the Lord God had made, which were addressed as good. The temptation itself seemed to be the main focus of Eve. There was no apparent surprise element in seeing a talking snake, or captivation of any sort. I had also read a reference to this from a website called Agapegeek which I agree with, that noted 1 Corinthians 10:13 "There hath no temptation taken you but such as is common to man: but God is faithful, who will not suffer you to be tempted above that ye are able; but will with the temptation also make a way to escape, that ye may be able to bear it." being all inclusive to humanity including Adam and Eve. Satan being an invisible force, attacking our minds.
The cultural elements I think influenced the reference to Satan as a snake is that the Israelites observed snakes fairly often, observing their hardships as a slithering creature eating dust, being trampled on, being held captive for magician entertainment, etc. Of course Satan describes himself as one walking around the earth. And snakes were symbolic at the time of Moses as a source of healing as well as being crafty, so serpentine symbolism didn't seem rare.
But, I could be totally wrong. It's just an opinion I hold at this time.