airports and environs are a target rich environment
especially and particularly to an attacker who m does not have escape as a priority (it doesn't even have to be a suicide attack)
Squealing at posters like little sheep as if not mentioning the obvious somehow makes you safe-ish.
ALL airport checkpoints are based on manners - you are politely ask to stop and be frisked, and politely, you comply. For some airports you are a short sprint from the gate and/or the aircraft. If someone decided to not stop, off they go! -It's not as if they have to be buzzed through, one by one, by someone sitting securely on the other side.
Undoubtedly in this case, the operators plan was to penetrate deeper into the airport, when challenged,they terminated in option B.
In this case the security system worked, the threat was identified and it was intercepted or met. The problem is that that still resulted in 40 or so dead.
Airport design is fundamentally flawed when presented with security questions.
A sports Arena has a somewhat better model as they are designed to allow for the ingress of a large number of individually authenticated individuals (with the awareness that a portion may be actively trying to get in w/o paying)
With airports, that was never the design concern, all the security structures have been bolted on after the fact and it shows.
The greatest threat is copy cat attacks, luckily, the Al Qaeda terror threat is greatly overblown, otherwise we would be up s*t creek