If there's really "no resistance" that would rather suggest that the US has targetted the wrong farms, ones where there in fact are no enemy fighters. It wouldn't be the first time. Only a couple of days ago the was an "incident" described here where 11 civilians were killed, five of them children, one six months old, were killed in an airstrike.

If this time they have actually identified the right target, "no resistance" would very likely imply that word of the attack was leaked in advance by friends of the insurgents in the Iraq military.

Foreign armies just cannot win this kind of conflict - you'd think they'd know by now.