Note that "several hundred ballots had been contested, largely by Amazon, and those ballots were set aside to be adjudicated and counted only if they were vital

Note that "several hundred ballots had been contested, largely by Amazon, and those ballots were set aside to be adjudicated and counted only if they were vital to determining an outcome". So several hundred ballots contested by Amazon, and the cynic in my assume that those were therefore probably all in favor of unionizing. This can change the 1100-to-463 balance significantly.