Abdullah lost four fumbles in 42 rushes. While not great, it's not like he's a fumbling machine, either - especially not for a true freshman getting his first taste of football at this level.
I think the timing of his fumbles are what makes them stand out more.
Thats 1 out of every 10 times he carries the ball. Thats absolutely awful at any level, freshman or not. Had Rex fumbled at that pace, he would have lost almost 30 fumbles last year (to put it into perspective). That's 30 extra possessions handed to the other team.
I hope you realize it's completely nonsensical to multiply statistics that way.
4 fumbles is a small number, period. One less fumble and it's 7% instead of 10. Two less and it's 5%, which would give Rex 15 fumbles last year instead of 30. If Ameer had 100 carries and kept up the 10% clip, then yes, we'd have something to talk about.
Here's another one for you. Ameer scored 3 touchdowns in his 42 carries. If we had only given him 200 carries, Ameer would've scored fourteen TDs last season.