If it was a cooked bone then yes potentially it might have splintered as opposed to just crunching and breaking.
I would give them hell, not only for throwing their trash over your fence, (but it could have been poisoned.)
Watch for blood in the stools, that will be an indication that there might be splinters swallowed and lodged in the intestine or stomach.
It might simply have been them thinking. . .
"Ooooh, next door has a big dog, and I've seen it eating bones before. . . .Here pooch have this nice big bone from our
Sunday roast"
Still, I would be having harsh words.