This is probably just a use of different words to not sound repetitive.
Then the BBC could have said something like “More than 500 people were slain in Gaza.” They should have used a word that implies that the more than 500 people were actively put to death somehow, like killed or slain.
Keep in mind that the BBC are journalists; they literally do this for a living. Even if it was an innocent mistake, which I 1000% do not believe it is, it would still be an egregious fuck-up. But we know it’s not a fuck-up…