It is already on the F.A.Q page at the bottom :
Game Stages & Settlement
"We track live price feed from 4 exchanges and average it. Visit our Pricing & Settlement page"
"Pricing Data
Bulls Vs. Bears platform is integrated with real-time price feed from the most liquid cryptocurrency exchanges.
 
Bitcoin price is currently derived from four different exchanges in equal parts: Huobi, Bitstamp, Binance, Coinbase.
In the event one of the exchanges loses service, we may automatically remove that exchange from calculation until it resumes.