Cuba determines who will or will not be their citizens by the legal means of their own determination. If they have legally established that a child born outside Cuba to a Cuban parent is a Cuban citizen at birth, then that child is a Cuban citizen. Specific to Cruz, I believe that his father expatriated and that this means Cuba no longer had any legal basis to claim Ted Cruz as a citizen, even if the operation of their citizenship laws would normally have claimed such a child as a citizen. Others may disagree, obviously.
[[Cuba determines who will or will not be their citizens by the legal means of their own determination.]]
Like I told Cdbolt, I believe that it has been found that a child born to a sovereign us citizen is a us citizen unless the parent allows the child to be sent abroad for citizenship in the other parent’s country- in which case I believe the parents would have to renounce their child’s citizenship here-
I may be wrong, but I believe US citizenship status of a parent trumps the foreign parent’s citizenship in another country- until the us citizen agrees to relinquish-