What is the difference between ETH withdrawal sent from a smart contract and from using native ETH chain?

In the Nexo withdrawal page it is written that "ETH withdrawals are sent from a smart contract (Bitfinex, Huobi and Hotbit do not accept ETH deposits sent from a smart contract)".

ELI5, Can anyone let me know what is the difference eth sent from smart contract vs eth sent from using native chain? Can the transaction be reversed or hacked since it was sent using smart contract?

thanks