The previous record is a matter of record: +7.5F in December, 1978. A few summers ago, we had a very warm week and we hit +7.0F in the middle of several days of above-zero temps. While I'm not a Global Warming denier by any means, the specific cause of these record and near-record temps is weather - specifically large masses of warm(er) air coming in from the coast.
Normally, the weather at Pole is so predictable it follows a simple pie chart hanging up in the Meteorology office - the chart divides the wind direction into dominant categories such that you can look at the reading from the wind vanes and make a pretty good prediction of the present and impending weather (mostly, winds out of Grid North bring in clearer and drier air; winds out of Grid West are warmer and moister; and winds out of Grid South are infrequent and bring unsettled conditions). This is in part because most of the time, the air movement is katabatic, meaning it's rolling downhill, and the terrain around Pole favors winds from Grid North. While thermally-induced winds are not unknown, they aren't the dominant force. It takes a lot of energy to disrupt the usual patterns; that's part of what "Global Warming" means - the entire atmosphere has more (thermal) energy, so there's more available force to create disruptions on a global scale.