Well said.
Denying that intelligence has a hereditary component doesn't make it so.
Of course this doesn't mean that every smart couple will birth nothing but smart kids nor that every stupid couple will birth nothing but stupid kids.
But lets say for the sake of argument that if 90% of all births to 2 intelligent people result in intelligent children, while only 10% of births to two stupid people result intelligent children... the guy would have a point, that meeting your spouse in college could result in a widening gap of intelligence.