I was thinking about this today. As I was surprised about the weight being given and thought that it might be a mailing weight and not the actual weight of the fabric. Just cause I like playing with numbers, I checked the 5 oz per yard and determined that if it is based on 60"x36" that if it was the same weight (2.69 oz) as the square yard that it would weigh about 4.5 oz per yard.
Another thought is that the "quilting" bandana fabric may not have the vivid colors on the back. I have some from years ago and i it seems like that was the case (lighter on the back).
Janey - Neat people never make the exciting discoveries I do.