Wrong. Just. Wrong.
Both of you, actually, but the ground can absolutely cause a fumble.
If a ball-carrier makes only legal contact with the ground - with only his hands, feet, or the football - and the ground knocks the ball out of his hand it is a fumble.
It's quite rare because they almost always make contact with at least an elbow, forearm, or wrist and are therefore down by contact but it is possible.
Clint Stoerner from the 1998 tennessee game says hi.