Fair or Foul?

[Cajun Reff]

coach pitch 7/8 y/o girls slowpitch softball, USSSA rules

Sec. 29. A foul ball is a batted ball which:
A. Settles on foul territory between home and first base, or between home
and 3rd base.
B. Bounds past first or third base on or over foul territory.
C. First falls on foul territory beyond first or third base.
D. While on or over foul territory touches the person of an umpire, a
player or any object foreign to the natural ground

RH batter hits the ball, ball goes straight down and hits in the batter's box just past the batter's foot and starts slowly rolling towards 3rd in foul territory, I am on the plate and I call foul ball. As it keeps rolling it hits a clump of dirt and kicks into fair territory just past the fair/foul area in front of home plate. Batting team coach says that ball should be fair and reading the USSSA rules it seems he may be correct.

Since I had already called foul ball, right or wrong the play is dead. This play has stuck with me since last night, did I interpret the fair/foul rule wrong? Is a clump of dirt on a poorly maintained field an "object" or is part of the "natural ground"