It is impossible to give an exact explanation without more context, but one meaning of 'to be thrown by ...' is if something is totally unexpected and confuses you so much that don't know what to say or how to react. If you could tell us the full context, we could give you a more precise and more helpful answer.

Hi :) good question To be thrown by something means to be disorientated. 'I was really thrown by the news' means that the news really disorientated me and I didn't know what to say or do! Confused would be another synonym :) I hope that helps! Liam