1) It's not just 1 pool. It is several miners not broadcasting who they are
2) Not sure where you are getting 20% it's 6.9% for the last 24H / 9.4% for 3D and 9.2% for 1W take a look at
https://btc.com/stats/pool-Dave
Oh strange, thanks for the link. I was getting this from Blockchain.com, guess they must be reporting inaccurate info again.
Thanks!