I heard somewhere that a surprising amount of people were killed by falling bullets (people shooting guns into the air, AA guns not hitting, misfires), during the Arab spring. where there a similar thing in WWII?
Yes, it certainly happened in WWII, although it would be impossible to get a quantitative analysis to that degree. Certainly there are plenty of examples to illustrate it though. In this old thread /u/bigglesworth_ and I discuss falling ordinance which you might find interesting.