Dramatic Irony - a literary technique by which the full significance of a character’s words or actions are clear to the audience or reader although unknown to the character.
 
In this scene, Twilight Sparkle accuses Shadow Lock of being reckless, because she thinks her friends are just down the hall, ready to barge in and help her if he attacks. However, what she doesn’t know is that Shadow Lock has already taken the precaution of trapping them in dreams from which they will not easily wake.