Wrong text message

In Korea, calling a elder's name without a title - like sister, brother, teacher, sir - is very rude behaviour. But most of students call teacher's name or nickname and speak ill of him behind his back. My class teacher was young and active man, so he liked hanging out with boys. After graduating high school, I met my schoolmates at a graduates' association and heard the story from my friend KK.
One day, he was going home on a bus and just looking on other people. At that time, a stranger came and sat in front of him. He was so surprised when he looked the man, because the man resembled to our previous class teacher SW. He observed the man for a moment, realised that the man was not the teacher and sent a text message to another classmate. 'Hey, I saw a man who looks like SW. It's greatly funny! I want to show the man to you.' Of course, there are many Korean slangs in the message. When he was sniggerring, the reply message arrived. 'Hi, KK. How are you? Sorry but the man is not me. I'm in school now :) - from SW.' He had sent the message not to his friend but to the teacher. KK said he hadn't shown up around school since that time.