In Iowa, which is the state the article is discussing, Huckabee won the 2008 caucus; Santorum won 2012. One would assume that they have better name recognition than say, Gilmore. Trump's been a celebrity for decades. Maybe I'm being naive/idealistic/whatever, but if I was being asked in a political poll who I was voting for, and I'm so low information that all I have to make a choice is name recognition, I would pick Huckabee or Santorum because I should recognize their names as politicians.
You fail to mention that we had record voter turnout this year up over 50% . These new voters never voted for Santorum or Huckabee. Plus of course those who voted this year are not exactly the same as those who voted in 2008 and 2012.
There is no question some of Trump’s poll numbers are from much higher name recognition.