I’m guessing Bitmain can’t pay for electricity with BTC.
Are there estimates of how much (fiat) money flowed into cryptocurrencies in the last year? It would have to be much more than $4B for Bitmain to be able to sell $4B worth of BTC and still see the 1000% gain.
The daily volume at the beginning of 2017 was $200M USD.
The daily volume at the end was $8T USD. $4B over 365 market days is somewhere between 1-4% of the daily market.
If liquidating their bitcoin tanked the market in 2017, it wasn't too noticable.
a) I think you're mistaken. $4B per annum is unlikely to move the markets much.