Leaving Korea to visit China on the way home

I'm leaving Korea on March 2nd and not returning. I want to get a tourist visa to China but an agent has said I cannot get one because I do not have 6 months on the arc. But I am not returning to Korea so why is this necessary? On the forms I didn' see anything about arc details. I have more than 6 months on my passport and I have proof of onward travel. What more do I need to show?