My understanding is that all numbers in the dump correspond with Facebook accounts, so this shouldn't be the reason.
Another option would be that someone else has that number listed for their account. Has Facebook always required confirmation that a number is valid? I saw one my friends' numbers in the data except the account had a different name.
Another option would be that someone else has that number listed for their account. Has Facebook always required confirmation that a number is valid? I saw one my friends' numbers in the data except the account had a different name.