Sure, but if the passengers were escorted landside, why did they then re-screen everyone? Surely only those passengers transiting to other flights would need to be re-screened and the rest could have been let go.
It doesn't say anywhere that all passengers were rescreened. Everyone was escorted off the plane, through airside to landside. It would then indeed have been only those transferring on that would have required rescreening back to airside. Anyone terminating in MEL would have been let leave.