If there is a "clear link between stolen passports and al-Qaeda-linked terrorist activity," and your country failed to use an international police force database that lists stolen passports, and checking the database took only 2-3 seconds, and the information could get about 100 or more hits per month for a small country, would you feel good about your country's anti-terrorist efforts?
Neither would I.
And yet, neither the UK nor the US uses the InterPol stolen passport database, according to the InterPol head Ronald Noble. Switzerland checks it about 300,000 times each month and gets about 100 hits. It is not far-fetched that terrorist infiltrators would use stolen (or forged, although those are vastly more difficult to use) passports to enter a target country.
Really, if the writers for the CBS show Numb3rs can come up with that notion, it's not that far for the terrorist mind to stretch.