According to Wikipedia, the population of the entire Gaza Strip is about 2.3 million. 11k people is about 0.5% of the population. The 9/11 attacks killed about 3,000 people out of a population of approx. 300 million, i.e. 0.001%. If my math is correct, that would this death toll equal to about 500 9/11s.
I don't even want to know how they extract that sample.