It was an Ethereum multisig smart contract.
In Bitcoin, multisig is simple and straightforward, easy to verify on a hardware wallet.
In Ethereum however, the simplest of smart contracts, even for a simple multisig set up, are harder to verify on a hardware wallet, creating more opportunities for such vulnerabilities.
Here is an article with more details about the hack:
https://www.ledgerinsights.com/bybit-hack-phishing-involved-plus-how-to-prevent-similar-hacks/