Coinbase will run a network which developers can use for storing game state (think in-game items), and the transactions that this network runs are regularly sent to Ethereum a snapshot and anyone can provide cryptographic proof if they see that Coinbase submitted invalid data and force the network to not accept that bad data (though that process probably not implemented yet and its unclear how the economics would work if Coinbase can't be financially punished for fraud like typical layer 2 validators).
This provides good security at the cost of decentralization, but you aren't held hostage by the centralized actor (Coinbase) like you'd be in a traditional centralized system.
This might mean that these games will have the ability to use each other's state and have any level of interoperability that each developer chooses, and we don't have to fully trust that Coinbase isn't cheating the users or devs.
Because this is a network that's secured by Ethereum, assets can also be moved from this network to the main Ethereum network if users want.