The Lord created us in His image and likeness, and we are the image of the Lord, and He does good and all of us have this commandment at heart, do good and do not do evil. All of us. 'But, Father, this is not Catholic! He cannot do good.' Yes, he can... "The Lord has redeemed all of us, all of us, with the Blood of Christ, all of us, not just Catholics. Everyone! 'Father, the atheists?' Even the atheists. Everyone!" We must meet one another doing good. 'But I don't believe, Father, I am an atheist!' But do good: we will meet one another there."
OK. I have no spies in the Vatican so this is conjecture of the highest order. But here's what I suspect happened.
The Pope didn't quite say atheists could go do to heaven. He made - or at least tried to make - a subtly different point. He said Christ redeemed
atheists just as he did Christians. Catholic soteriology is ridiculously complicated. They've had a long time to make it so. Here
is a pretty full explanation but be aware its heavy going. In short, though, redemption and salvation are different, though highly related, things.
The idea that Christ redeemed all of mankind is far from new. Read up on the Jesuit "Karl Rahner" for more details. It's orthodoxy, in short. Not in debate (within Catholic dogma, obviously). Its even biblical - 1 Timothy talks of Christ giving himself as "a ransom for all" and the Catechism accepts this to some extent - CC 2125
is the relevant bit.
So, what I suspect has happened - and again I stress this is a guess not based on anything much - is that the Pope gave a homily talking about that aspect in incredibly unclear language. A load of news sources that, understandably, don't employ theologians ran with a Protesstant interpretation - where, in a lot of denominations - redemption is sufficient for salvation rather than simply necessary as it is in Catholicism. So they took the Pope's words as saying that atheists can go to heaven. What he meant
to say is that there is no intrinsic attribute of atheists preventing them going to heaven.
So, now the Church is doing a frantic clean up job. A "No, no, that's not what we meant"
ETA: Incidentally, contrary to the Huffington Post article you link - Thomas Rosica
isn't a Vatican spokesman.