An international student who majors in engineering drops by the engineering department office and asks the secretary, “Can you tell me where the English department is?” The secretary smiles and responds, “I don’t know, actually. It’s probably somewhere in the Humanities Building. Do you have a campus map?” The student turns around and leaves. The secretary is taken aback and feels slightly uncomfortable. She wonders why the student left so abruptly.

(...)

People who interact with ESL students have commented that some seem to express gratitude excessively for small considerations, even to the point of embarrassing the person they are speaking. Others seem downright rude because they do not say thank you when they are expected to.

(Celce-Murcia, M. 2001.)

In the context of the first paragraph, the expression “taken aback” means the secretary was