Other than, you know, misreading the Duckworth-Lewis charts. I’m sure he’ll earn a fair amount of criticism for that, but it’s more forgivable than his other big mistake: he didn’t have faith in his team.
Understand what happened here: Dyson thought the West Indies could take advantage of the light offer; that is, he thought they could get home without having to travel up the driveway. He saw what he thought to be a victory, and rather than reaching the original target, he figured he’d do it that way.
But the light — according to Cricinfo’s commentary — was only a “little bit murky,” and conditions didn’t seem unplayable at all. Had he not gone through D/L, had Dyson just felt secure in the ability of his men to get the 20-odd runs left, this may not have happened. After all, the West Indies were only 1 run behind…they could have won this the old-fashioned way.