I believe the framers would have thought that people would naturally understand that if the the Constitution says (forgive my paraphrase):
1. The president must be a natural-born citizen. And . . .
2. The vice president shall assume the office of the presidency in the event of the death or incapacitation of the president.
...that the electoral college would not elect, nor would the Congress certify the placement of a vice president not qualified to be president.
As the Vice President was originally the candidate who came second in the EC vote for President, the prof's loophole didn't apply