I suspect Hamas aren't stupid and probably used old fashioned methods of getting plans around for this like messengers and paper and pencil. Gaza is a pretty small place and easy to slip into the crowd.
I think you're partially right that policies of the right-wing governments in Israel (apartheid, normalizing relations with Arab countries while ignoring Palestinians) likely helped the Palestinian crazies grow and thus in effect those people in power are partially responsible for this attack on Israel people, whether they realize it or not. I'm not condoning the attack in any way. But responsibility for the atrocities can be shared between actors on many sides.