Jolin Tsai posted a picture on Weibo saying that he was like a quiet chicken, and then discovered that the chicken has a special meaning in the mainland, so he quickly deleted Weibo.
Unfortunately, this Weibo was seen by a netizen called “Essence Knight”, so the term became popular. Generally accepted is this source.
Quiet like a chicken is a short form of “quiet like a chicken”. The term of the fan circle is to make fans shut up when they should, and talk less when they shouldn’t. Or even chattering all the time, but when the results are announced, the noisy fans will be quiet.
There are similar words with quiet as a chicken: lonely as a dog, and behaved as a goose. These three words are often used together.