I don't think the ballots can be linked back to a voter. If they are referring to mailed ballots, the ballots were taken from the envelopes, that could identify a voter, and added to ballots cast at a polling location, which do not identify a voter. They would be in separate piles in any post-election audit. Although a polling place records who votes, how you vote is supposed to be anonymous. Now if those mailing envelopes are kept, and those numbers don't agree with the number of ballots that are supposed to correlate with those envelopes, that would be a big red flag.