I think he was more pointing out that that huge crowd of people that can't evacuate the area easily or quickly is actually a pretty prime target for terrorist mayhem.
Absolutely. If I was a suicide bomber, this is exactly where I'd explode my bomb. I reckon I could get a devastating quantity of explosive in a carry-on bag and detonate it in the snake-line. Also get an accomplice to do the same in a check-in line with a full-size suitcase packed with HE.
While it might not have the glamour of bringing down an aircraft, no matter where the TSA or local equivalent move the security line to (pre-security security, pre-security security security...), passengers are still vulnerable to this attack. I can't see a practical defence against it.
It's truly chilling that they could do this trivially, tomorrow.