The usage of とは in 緊急招集とは、おだやかではないな

Question

From what I understand, とは can be used to "define" things. So does this mean that it can be used to expand on what comes before とは/というのは and that which comes after will explain the speakers view/opinion/etc on what comes before?

So how does it work in the example where the speaker has been called out to an emergency meeting without being told what it was about and says

「緊急招集とは、おだやかではないな」

Answer 1

「[緊 急 招 集]{きんきゅうしょうしゅう}とは、おだやかではないな。」

= "An emergency call-out is pretty disquieting, isn't it?"

This 「とは」　is not for defining something. Both speaker and listener know exactly what 「緊急招集」 means already.

This 「とは」 is to express a surprise, anger, excitement, etc. It is like an emphatic kind of topic marker. You did not expect it coming.