sorry for being dumb but if someone has modifed the code and you run it in a offline computer how does the hacker gain your information? how is it sent to him becase there is no internet connection to send the data or he cant remote control your computer because theres no internet access.
The idea is that you downloaded software from the hacker and use it to generate your wallet. Since he designed it to produce specified outputs, it generates private keys that he can recognize in the blockchain. So it doesn't matter that your cold wallet generating system is offline.