Adam Clarke on Numbers 16:46

The plague is begun - God now punished them by a secret blast, so as to put the matter beyond all dispute; his hand, and his alone, was seen, not only in the plague, but in the manner in which the mortality was arrested. It was necessary that this should be done in this way, that the whole congregation might see that those men who had perished were not the people of the Lord; and that God, not Moses and Aaron, had destroyed them.