Caitlyn Auto While Stunned

Cait Auto while Stunned
I don't understand why she got to auto.
In the clip, I (Vayne) condemn Caitlyn into a wall and she autos while the stun timer is above her head and ticking down. Caitlyn has 1.7 attack speed at this point in the game which is possibly the only excuse I can possibly think of for getting this auto off, but she starts the auto after getting stunned. I have no real idea why she would be able to get this auto off.
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