If reviewed I'm assuming they ruled ground caused the fumble?
"The ground cannot cause a fumble..." This universally known bit of announcer-speak is, I'd say, 98% accurate - but it's not the actual rule.
The actual rule is, the down ends at the instant the ball carrier is down. And he's down when any body part besides hands or feet touches the ground. So 98% of the time, if the ball pops out due to contact with the ground, it's popping out
due to one of those body parts striking the ground. No fumble.
But here's a case when that fan aphorism is not the truth: Suppose a quarterback is palming the ball in one hand, and he stumbles and braces himself with both hands to avoid falling down, and the ball pops out. No other body part touched the ground. That is definitely a fumble, and the ground definitely caused it.