Why is your English that good?

During a conversation with students about the differences between Korean and American high schools the following question was asked.

Student: "What is the Illuminati?"

Me: "Uhh...it's complicated...umm...uhh....(confused face)"
(3 second pause)
Me: "I'm not really sure but..."
Student: "Ok" (shoulder shrug, moves on to other topics)

As this was happening all I could think was "Why is your English this good?!  And where did you even hear about this?!"  Clearly I was not prepared for this situation.