Why did 'Voice Avengers' fail their prank on Sunmi?

The 'Voice Avengers' crew failed their prank on solo singer Sunmi. 

 
The September 26th Chuseok special followed comedian Byun Seung Yoon as he interviewed Sunmi pretending to be a Chinese reporter. When asked if she knows Chinese, Sunmi responded, "I've learned it before."

Still, the interview in Chinese went on, and Sunmi looked incredibly confused by Byun Seung Yoon's questions. She then yelled, "What is this?" after realizing he was speaking gibberish instead of actual Chinese.

Did you know Sunmi studied Chinese?