They're probably correct (for once) NOT terrorism. If it were there be a heckuva lot more dead and injured. I'll bet it was something else, maybe work evaluation related or personal relationship issues (don't ask don't tell?). But not Jihadi, of that I'm sure. If the body count rises to 12 then it means something else.
Practice run?
But they were stopped at the gate. Had they gotten through it could have turned out worse. Once the identities are released we can better assess the situation.