Flat Artifact Piece---was it ground?

A friend of ours dropped by with an unique artifact piece he found in a cache which contained two core pieces weighing around 3 lbs., three spalls, and two worked preforms that are around 4-5 inches long. This piece was around 8 1/2 inches long and 1 inch thick, all the pieces were covered in cortex. One side was fairly flat across for around 6 inches of the face with some flakes removed  around the edges. The other side was completely flat almost across the entire 8 1/2 inch face and had not been flaked. It was so completely flat it looked like a piece would if ran through a rock saw. There appeared to be very small drag marks across the flat side as if it was ground.(unable to show these marks in the picture, actually 3rd picture down you can see marks running long ways the length of the face).

This piece is made of NC Rhyolite which sources of can be found about 30 miles from where this artifact was found.

It is known that Type 1C danish daggers and egyptian gerzean knives were ground. We have speculated in previous articles that the Sweetwater biface was also ground. 

Below are some pictures, so what do think, was this piece ground flat?  If so, was it intended to be a preform? Or what was the intended purpose? Or if it wasn't ground, how did it get this completely flat?


This is a picture of the completely flat side, as you can see from the ruler placed on top of it, it is as flat as the ruler all the way across.

 

 This is picture of the completely flat side showing the face, as you can see the flatness runs almost entirely the whole length of the piece at around 7 of the 8 1/2 inches total.

 

Same side without the ruler. 

This is a picture of the face of the other side which had some flakes removed around the edges. It was fairly flat as well across 6 inches of the face, although not completely flat as the other side.

 

Same side without the ruler.