Bitcoin Cash has a separate blockchain (and peer-to-peer swarm, etc) but uses the same address format and checksum as Bitcoin. Bitcoin Cash did that on purpose

Bitcoin Cash has a separate blockchain (and peer-to-peer swarm, etc) but uses the same address format and checksum as Bitcoin. Bitcoin Cash did that on purpose so people's addresses from before the fork would continue to work if they moved to BCH at the fork. Personally I think they (BCH) like the confusion because it keeps people talking about them where Bitcoin is talked about (never mind the confusingly-similar name). Coinbase technically could make the addresses they show be able to receive both BTC and BCH funds, but it would be more complexity on their end as their BTC and BCH support would no longer be separate systems. There is a plan for Bitcoin to get a new type of address format eventually (BIP 173, "Bech32"), built specifically for Segwit addresses, so this problem will eventually be addressed. Well, it will be fixed until the next Bitcoin Cash Gold Deluxe Whatever fork shows up...