You're probably looking at BCC futures prices.
Here's the best way to look at what will happen. Right now we have a single blockchain, the Bitcoin blockchain, there is no BCC / "Bitcoin Cash" yet - so far so good . . ?
On August 1st there is a good chance that the UAHF (user activated hard fork) will be implemented anyway, in spite of the recent BIP 91 activation . . so . .
If that happens the Bitcoin blockchain will "fork" into 2 separate blockchains and a "new" coin is born - one blockchain continues as BTC and the other one starts the new coin BCC .
The interesting thing is this - at the moment the fork occurs, the balance you hold in BTC at that moment will be the balance you also hold in BCC
What you do with those BCC could be several things, most of which will be driven by how successful the segwit implementation seems to have been, i.e. the more successful segwit is, the less valuable BCC will likely be, and of course the opposite is true as well, if there seem to be issues with segwit I would expect the value of BCC to go up :)
So yeah, I said I would just hold mine, but of course if things go wrong with segwit and BCC goes sky high, I'll probably end up selling anyway :D
Hope that explanation was clear (and hopefully helpful?)
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The 1:1 correlation is simply the number of BTC to BCC you will get, not a value of any kind.
It is vital to understand that once the chains would split, they exactly that - Split - they are separate chains and there is no trading back and forth . .
There are certain attacks which would seek to do essentially what you are describing, but safeguards are being implemented against "replay" attacks, and of course "double-spend" attacks.
So hopefully now, if you picture 2 separate blockchains, one for BCC and one for BTC , with no way for coins to move directly between the 2 chains, it will explain things for you :)
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I've done my best to explain it mate, perhaps a bit more research on your own part focused on the UAHF would be more productive for you - good luck!