No hint of shomer shabbos contributing. Which version is accurate?
Her intro mentions it. The gate was locked. That gave them time for the tiny response team to get arms and fight back. That fight bought more time for reinforcements to come join the fight. Had the gate been open, the terrorists would have been in the kibbutz going door to door before anyone could fight them.
They also treated survivors from the music festival, so not only did the gate save Sa'ad, it also created a refuge for survivors to escape to and get some sort of medical treatment.