Where did you see wBTC at $20k? That would be a great arbitrage opportunity since you can still unwrap it (redeem/burn) for real BTC onchain. 
I took some screenshots earlier today and posted about it on the German board. It looks like WBTC had a significantly lower price than BTC for several (!) hours. I just think that no large orders were possible during this period. If there were, some users certainly made a killing.
It looks like CMC already fixed their chat. This is what it looked like this morning:
Source: CoinMarketCap, 7 day WBTC Chart. https://coinmarketcap.com/currencies/wrapped-bitcoin/