Here "cloud" means a swarm. The author speaks of the army as if it were a swarm of locusts to emphasize how many soldiers there were. (See: [[rc://en/ta/man/translate/figs-simile]])
This can be stated in active form. Alternate translation: "Their camels were more than anyone could count" (See: [[rc://en/ta/man/translate/figs-activepassive]])