"Enchanter" est bien une keyword ability, mais voici ce que dit le texte de la capacité :
702.5. Enchant
702.5a Enchant is a static ability, written "Enchant [object or player]." The enchant ability restricts what an Aura spell can target and what an Aura can enchant.
702.5b For more information on Auras, see rule 303, "Enchantments."
702.5c If an Aura has multiple instances of enchant, all of them apply. The Aura's target must follow the restrictions from all the instances of enchant. The Aura can enchant only objects or players that match all of its enchant abilities.
702.5d Auras that can enchant a player can target and be attached to players. Such Auras can't target permanents and can't be attached to permanents.
Bref, il y a bien marqué "target" dans la définition de la capacité, mais uniquement parce que la capacité sert à restreindre ce que l'aura pourra cibler et à quoi elle pourra s'attacher.
La règle qui explicite ce ciblage est bien la règle du sous-type Aura :
114.1b Aura spells are always targeted. These are the only permanent spells with targets. An Aura's target is specified by its enchant keyword ability (see rule 702.5, "Enchant"). The target(s) are chosen as the spell is cast; see rule 601.2c. An Aura permanent doesn't target anything; only the spell is targeted. (An activated or triggered ability of an Aura permanent can also be targeted.)
303.4. Some enchantments have the subtype "Aura." An Aura enters the battlefield attached to an object or player. What an Aura can be attached to is restricted by its enchant keyword ability (see rule 702.5, "Enchant"). Other effects can limit what a permanent can be enchanted by.
303.4a An Aura spell requires a target, which is restricted by its enchant ability.
303.4b The object or player an Aura is attached to is called enchanted. The Aura is attached to, or "enchants," that object or player.
303.4c If an Aura is enchanting an illegal object or player, the object it was attached to no longer exists, or the player it was attached to has left the game, the Aura is put into its owner's graveyard. (This is a state-based action. See rule 704.)
303.4d An Aura can't enchant itself. If this occurs somehow, the Aura is put into its owner's graveyard. An Aura that's also a creature can't enchant anything. If this occurs somehow, the Aura becomes unattached, then is put into its owner's graveyard. (These are state-based actions. See rule 704.) An Aura can't enchant more than one object or player. If a spell or ability would cause an Aura to become attached to more than one object or player, the Aura's controller chooses which object or player it becomes attached to.
303.4e An Aura's controller is separate from the enchanted object's controller or the enchanted player; the two need not be the same. If an Aura enchants an object, changing control of the object doesn't change control of the Aura, and vice versa. Only the Aura's controller can activate its abilities. However, if the Aura grants an ability to the enchanted object (with "gains" or "has"), the enchanted object's controller is the only one who can activate that ability.
303.4f If an Aura is entering the battlefield under a player's control by any means other than by resolving as an Aura spell, and the effect putting it onto the battlefield doesn't specify the object or player the Aura will enchant, that player chooses what it will enchant as the Aura enters the battlefield. The player must choose a legal object or player according to the Aura's enchant ability and any other applicable effects.
303.4g If an Aura is entering the battlefield and there is no legal object or player for it to enchant, the Aura remains in its current zone, unless that zone is the stack. In that case, the Aura is put into its owner's graveyard instead of entering the battlefield.
303.4h If an effect attempts to attach an Aura on the battlefield to an object or player, that object or player must be able to be enchanted by it. If the object or player can't be, the Aura doesn't move.
303.4i If a non-Aura permanent has an ability that refers to the "enchanted [object or player]" that phrase doesn't refer to any object or player.
Bref, si tu prends le temps de lire la définition de la capacité "Enchanter", tu te rends compte qu'il est question de cibles. Mais pour réellement connaître la règle, ce n'est pas du côté d'une capacité qu'il faut regarder mais des règles associées au sous-type Aura.
Ce qui fait donc effectivement de cette règle une exception.
