While Israel got far out ahead in its vaccination campaign early on, it’s current rate of vaccination isn’t particularly high, still below 65% of the population has completed the full course of vaccinations.
Heard immunity estimates have always been at the 70-85% level, so there’s no reason to believe Israel was immune to such outbreaks, especially with a more virulent variant such as delta. All that matters is whether the replication rate is above or below one, if you don’t have the level of population immunity to keep that R value below one, you will see outbreaks.