Is there any meaning of "frown" other than angry? The sentence below is from a book but I see no reason the teacher gets angry at a map of Europe. It just didn't fit in the context.

The agent came for me during a geography lesson. She entered the room and nodded at my fifth-grade teacher, who stood frowning at a map of Europe.

Thank you,

Frown is most commonly associated with being sad. I can see it being used for confusion or displeasure as well.
I think this definition works well enough:

to contract the brow, as in displeasure or deep thought; scowl.