Bitcoin Cash, money out of thin air - too good to be true?

My first post here at Steemit, so be gentle :)

As a new guy in the world of crypto currencies, can someone please help me explain how Bitcoin have managed to maintain it's 2700$ per BTC while Bitcoin Cash have achieved 500$ per BCH?

My logic before we went into the fork two days ago, was that the sum of the market cap on BTC and BCH should be constant, at BTC's level of 45$ billion before the fork (unless people started trading their altcoins for BTC or BCH).
However the case, roughly two days into the fork, is that BTC have maintained it's 45$ billion market cap and BCH has pumped up a 8$ billion cap and the altcoins over a broad have gained or maintained their cap, how can this be?

The only way BCH's 8$ billion market cap could then have appaired was if the 8$ billion had been added by investors in cool cash - but can that really be the case? After all if we add the market cap of the top 10 currencies together we are under 100$ billion in market cap, which would mean that the crypto currency market had grown 8-9% over night. To me that seems unlikely.

This is not to sound conspicuous, but I just don't get it, everybody seems to have gained and no one seems to have lost - that is alarming and why I wonder if it is too good to be true.

What is our thoughts, did the crypto market just got 8-9% better or are we inflating a balloon just waiting to burst?