That was a Dec 12 poll. almost two months before the primary. It was likely accurate at the time. Where you can’t seem to understand polls is that you assume they are predictive of the future. They are not.
In 2011-12, with Newt leading the polls, all six other candidates unleashed a relentless anti Newt campaign and changed the electorate.
Strange isn’t it, that this is not working with Trump. This is one strange campaign.