From what I understand there were a few armed civilians, but I could be wrong. I'd like to know more specifics of the case...
From the Washington Times...
Ex-Royal Marine saved 100 during al Qaeda attack at Kenya mall: report
..
(edit) and an article from the blaze that mentions the sidearm (with pic):
FORMER BRITISH MARINE ‘SAVED 100 PEOPLE’ FROM KENYA MALL ARMED ONLY WITH A HANDGUN
..