You are right, but it is not ruled out entirely because they used Wolf and Abel prize in the contenders group, which are awarded for a lifetime of work in mathematics and therefore biasing the contender groups.
And, as I already pointed out, the non-award-winners must by definition be different from award-winners and cannot control for unobserved baseline differences. Even more so if those prizes are, as is only sane, intended to reward different things than what the most prestigious prize in the field already rewards...