In addition to the other cm2187's accurate observation that this may be literal survivor bias, the other potential explanation is whether the control group was well designed.

Israel is currently ~50% Sephardic Jews, descendants from Middle Eastern/North African peoples. Holocaust survivors are almost all Ashkenazi Jews (European ancestors). If the study was comparing Ashkenazi Jews in the test group vs a control group that was majority Sephardic, it's possible the differences in lifetime was due to some cultural or genetic differences between the two groups.

The study doesn't seem to account for this confounding variable.