Rubio is not an “anchor baby” - his parents were legally in the United States at the time of his birth. That meets the definition of Natural Born Citizen - both by the definition of the phrase at the time it was written (the English common law definition) and also by adjudication in the courts. “Anchor baby” refers to babies born to people not legally within the United States to try to allow them to stay by virtue of the fact their child is supposedly a citizen by right of birth...a matter that has actually never been fully adjudicated.
Rubio’s parents were not citizens when he was born. He is an anchor baby.