I think you guys are referring to two different accounts of the same incident. Hamas claims Israel gunned down Gazans (not sure how we got to hundreds, I don't think even Hamas claimed that) and Israel claims the Palestinians mobbed the trucks and got run over as the trucks were trying to get away.

The Hamas started calling this the "Flour Massacre" since it has a certain ring to it. Given where the information is coming from I suspect it's not true. Like anything else, we don't have independent information. The IDF did investigate this as well and admitted to shooting at people approaching their security vehicles (that were there to secure the aid delivery).