I don't know about FL. In CA, the ballots are (by colour too?) coded by party. It wouldn't be hard to know what the series of ballot serial numbers were that corresponded to GOP registered voters and other parties if the same happens in FL.
Mix in demographic data for precincts and a thorough statistical analysis can reveal the types of information they claim in the article.
Newz, my friend, what you say about color coding of ballots occurs only in primary elections... There can be no partisan difference in a general election.