The writer speaks of Yahweh causing birds to fall from the sky as if the birds were rain that Yahweh caused to fall. He compares the large amount of birds to dust. AT: "He caused meat to fall from the sky like rain, and there was so much of it that it covered the ground like dust" (See: [[rc://en/ta/man/translate/figs-metaphor]] and [[rc://en/ta/man/translate/figs-simile]])
No one can count the grains of sand. There were more birds than anyone could count, but this is an exaggeration: there were probably not literally the same number of birds as grains of sand. (See: [[rc://en/ta/man/translate/figs-hyperbole]])