Most, if not all of them.
Jews are only 2% of the US population. Even if all of them go to university it would be impossible for them comprise more then 10% of the college going population. (27% of the general population has graduated from college).
Of course 10% can be considered substantial if they present a unified front but that is rare with any group.
I understand what you're saying, but there are Jewish students, plenty, on every campus. He's just saying this to manipulate the situation. What a publicity whore he is.