Steel Wing specifically says in its description that it is an attack made with the pokemon's wings. Aerial Ace makes no such specifications.
Charmander being able to learn Steel Wing makes as much sense as Dratini being able to learn Dragon Claw. --- Zelos Wilder: "Demon Fang! Demon Fang! Demon Fang! Damn, I must be a genius! Double Demon Fang!"