I'm a substitute teacher

I was in the staff room today at lunch and saw a new face, which only meant they are substitute teaching. I struck up a conversation with him and then he asked, "What are you doing here today?" I didn't really understand the question but answered, "Oh you know, the same thing I do here everyday..." And then it dawned on me that he thought I was a substitute teacher as well. Japanese-American-Canadian's can be full time teachers too.