I think about that story a lot because I'd like to know what happened in those thirty minutes. Presumably they continued to discuss the situation, and Cook's opinion of it worsened to where he demanded immediate action. It wouldn't make sense for Khan to leave the meeting and have to be caught up later on the situation he'd flown to China to resolve.

Less likely possibilities: was Cook talking to someone in the other direction and only noticed Khan? Was he thinking to himself Khan should leave immediately but wanted to give him some time to make the call himself?