Despite having keen senses and perception, the dragon didn't notice a huge comet falling atop it. But how can a huge falling celestial object go unnoticed? That was actually the work of the fox's unique skill.
The unique skill, Mystic Artist, allows the fox to combine abilities and develop new techniques. Magic spells can be combined with art techniques; techniques can be combined with skills; and skills can be combined with the spells; and with themselves.
In order to hit her target, the dragon, with precision, she has to make her attack unnoticeable to the dragon. As she was casting her World Magic spell, she secretly applied a certain skill of hers to it.
By cloaking her spell with the Perfect Concealment extra skill, she was able to conceal the falling comet from anyone on the surface. Hiding the comet's fascinating, glistening tail from the world.