Earlier quoted context omitted.
I think he means on arrival in the US, not before you get on the plane.
I think his point is that some other countries don't take the latest TSA requirements seriously, and if you come from one of those countries, the TSA will screen you because of that.
Imagine a daycare center that had a policy of running background checks on its employees only once they quit. Would you feel like they were taking the children's safety very seriously?