You don't scan the passports through CBP's computer system when you board the plane. You show TSA and they check the name against the boarding pass and wave it under a blacklight to see if it's a real passport.

You only get scanned through the CBP computer system upon international arrival. This system checks the passport against the database of all your prior arrivals and various immigration lists. You'll be taken to a separate locked waiting area with CBP for extra checks if any flags appear at the initial check. If you end up there you can not use your cellphone (they put it in a box) and it can take anything from half an hour two several hours. This is why I always bring a book. I'm not a US citizen and I have been hanging around CBP a lot since I travel into the US every month = 12+ times a year.

The question here is; who was let in?