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 guess he saw that information in WO because he is active there, and someone posted today that this token has been in a bit of a problem in the last 7 days. Honestly, I don't pay attention to any variations (forks) of BTC, not even to this wrapped version.
No, I did not see this post until now. I saw the chart in Coinmarketcap today, and I just checked again and was shocked. They manipulated the chart for an unknown reason. I am not the only guy who has seen WBTC de-pegged. It was de-pegged for almost all day and now regained the peg. The main problem is they manipulated the chart. They removed actual 24h low data and adjusted it with real BTC. As far as I know, this happened because of a multichain sell-off.
The line chart might just be showing a moving average to smooth out extreme fluctuations. If you change the view to the candlestick chart it will still show you how low the price went.
WBTC proof of reserves are published online. As long as the custodian holding the collateral isn't facing issues, like FTX was when soBTC depegged, I would expect the price to return to normal.
It is a token minted with their promise to back 1 Wrapped Bitcoin by 1 bitcoin. You never know what they do with the custodian party to back their token. They can back the token with less than 1:1 ratio and the token can be de-pegged when it is brought to the light.
Their team advertise that they do it to bring Bitcoin to DeFi but why Bitcoin need to exist in DeFi which is for altcoins?
Wrapped Bitcoin is a token, an altcoin, not Bitcoin. You don't have to buy the token and have risk that it will be de-pegged. If you want to join DeFi, buy any token on ERC20 like USDT, ETH and you have that token on its main chain.
Buy WBTC and think you have BTC but it's not bitcoin.
Their team advertise that they do it to bring Bitcoin to DeFi but why Bitcoin need to exist in DeFi which is for altcoins?
Wrapped Bitcoin is a token, an altcoin, not Bitcoin. You don't have to buy the token and have risk that it will be de-pegged. If you want to join DeFi, buy any token on ERC20 like USDT, ETH and you have that token on its main chain.
Buy WBTC and think you have BTC but it's not bitcoin.
USDT is just a wrapped version of USD. It is not real dollars. The same thing with the ETH that is traded on decentralized exchanges. It is actually wrapped Ethereum because the native token isn't ERC-20.
There are many reasons why someone might want to use wrapped BTC on other networks. Trading volatile tokens against the price of other volatile tokens is not very practical. Also, a lot of these tokens don't have great liquidity. DEXs would be dead without these wrapped currencies.