Because Bitcoin Cash is forked from Bitcoin, what happens if two separate users create a wallet, could their address potentially be the same? Let's call that address xyz. Then if someone sends money to xyz which blockchain would it go to?
Addresses are not really a thing as far as blockchains go - they mostly just care about the keys involved (or in the case of Bitcoin and Bitcoin based networks, the locking script which locks an output to be spendable only by a certain [set of] key[s]).
Since the key generation process relies on entropy, and does not rely on the network you are creating the key for, it is possible, and highly improbable, that two people are able to generate an identical key.
It is so improbable that no wallet I'm aware of actually checks for key reuse on the target chain. It's simply something that is not likely to occur, provided you have a good enough source of entropy.
Note that even if you do end up generating (or manually copying) a key across networks, the actual "address" may still be different, since Bitcoin uses base58/bech32 addresses, while BCH uses base58/cashaddr addresses. This is merely an encoding, however, and does not change the underlying key required to spend the outputs.