How to write "bei wu long" in Chinese and what is its origin?
I'm pretty sure that the " Bei Wu Long" is "摆乌龙". "乌龙" in Cantonese sounds like "own goal" in English. You know own goal is a big mistake, right？

It is a long story. According to this website, is is original from a folk tale in Canton. Once upon a time, there was a drought. People prayed to the "青龙"(Green Dragon) because it can bring rain. However, at last it was the "乌龙"( Black Dragon) who bring disaster that answered to them. The situation became worse.

Then in 1960s, journalist in Hongkong use "乌龙" to describe the "own goal" in soccer game because the "乌龙" sound similar in Cantonese to "own goal".