If I read correctly, the argument is that Rubio fits the ‘concept’ for NBC of parents or child having relinquished allegiance to a foreign government i.e. Cuba. The parents by intent (I believe both parents were not yet naturalized at time of Rubio’s birth ) and Rubio by birth ( I’m taking that Rubio was born on USA soil). The matter of ‘concept’ is certainly valid for discussing the considerations of the Founding Fathers. There is much in the records since that time with some court records. My personal belief is that the ‘concept of allegiance’ was intended by the Founders to be applied to both parentage citizenship and soil of parents. This belief is also based on the 1874 USA Supreme Court decision in the Minor vs Happersett that explicitly dealt with the ‘concept’ as envisioned by the Founders.
On this question I will defer to superior research. From what I have learned, it is plausible for it to go either way. It would not bother me at all if Rubio was considered to be a natural born citizen. Unlike Barack Obama, Rubio's father DID become a citizen.