It seems you're agreeing with the article even if you don't realise it.

The article says the attack was succesful, but not significant. A point you don't seem to oppose.

The point of the quote is that IF a terrorist organization was able to launch an actually crippling attack, they would have. Since they haven't, odds are they can't.

If you read on a little bit, he clearly states that this CAN change. But, for the time being, the abscence of a crippling attack is evidence that terrorists are not yet able to execute a such.