The information is based on exit polls. From what I have seen the numbers belie the story that there were less R votes than there should have been. In 2012 Romney got more votes than McCain did in 2008. Obama lost votes from the previous election, but still had more votes than Romney, especially where it really counted in the electoral college.
Of course you would have to trust the vote tallies from the FEC.
Per your citations, the claim is made for 3 million white voters sitting out the election. In all actuality that my be real. What does that necessarily have to do with the price of tea in china?