can someone explain the difference between this and just [node] ?
I think it is simply that if the clause before node is a noun, such as in this example, then you use 'nanode'. If it is a verb then you only use 'node'. As far as I know, 'na' seems to be related to the copula 'da', and can be seen in other similar circumstances such as 'nanoni'. Exactly why it changes to na instead of da I don't know. Contrast 'sou da to omou',and 'sou na node...'
な is 連体形 of 助動詞「だ」which inflect as だろ、で、だっ、だ、な、なら but な only connects to particles の、ので、のに.