It comes from what the customer service of Sanguosha said: "Our game is booming."
According to a query on Fantasy Mobile Games, Steam refers to the game Three Kingdoms. The reason why Three Kingdoms is called steaming is because the customer service of Three Kingdoms said, "Our game is booming."
"Three Kingdoms" is a tabletop game designed by the 2004 game major students of the School of Animation of Communication University of China. It is published and distributed by Beijing Youka Board Game Culture Development Co., Ltd. and was released by Hangzhou at the end of June 2009. Winger Network Technology Co., Ltd. develops online games.