I get up and see this:

BCH has gone from around $10 billion market cap to $30 billion market cap in a couple of days. Who the hell has some spare $20 billion to pour into BCH? Buffets net worth is around $77 billion.
I dont think this can only be explained to Roger Ver and Jihan Wu going all in on BCH. They must have persuaded institutional investors to get into BCH. Apart from scared people exchanging BTC for BCH.
I will HODL but this is serious.
If the price of an asset goes up 20b does not mean that 20b moved into it. U can create that price with a fe million if u wanted
You are right that it doesn't necessarily mean that 20b$ has been moved into Bitcoin cash, but you won't be able to add bilions to the market cap with millions, I guess that around 4-5 Billion dollars entered the cash market.
The market cap presents the total amount of tokens available (shares ) *last price, it doesn't mean that there is enough liquidity to buy all the shares at the last price, so if someone sell x amount of shares, it will probably cause the price to decrease/.