These two phrases mean basically the same thing and emphasize that destruction will begin at Heshbon. The fire refers to a destroying army. Alternate translation: "King Sihon led a strong army from the city of Heshbon" (See: [[rc://en/ta/man/translate/figs-parallelism]] and [[rc://en/ta/man/translate/figs-metaphor]])
The army of Sihon is spoken of as if it was an animal that ate up the city of Ar. Alternate translation: "destroyed the town of Ar in the land of Moab" (See: [[rc://en/ta/man/translate/figs-metaphor]])