No computer device is unhackable, and this statement cannot be argued. However, the private keys are not stored in a Bitfi at any point.

To put simply. Bitfi stores a set of algorithms that receive the salt & passphrase as an input, and signal it to the blockchain; if there’s a match, the wallet’s unlocked. Thus, there isn’t a need to store the key within the device.
In case a Bitfi is hacked, there’s no private key held within and thus no assets can be claimed by the hacker.