system
A chat on subreddit /r/NoStupidQuestions
human
Welcome to mythology.   


Also, when Cain killed his brother, he was sent out, to live *with other people*\--so who the fuck were they then?  


Mythology. None of it was real. Zero.
gpt
It doesn't say Cain was sent to live with other people. It says he left and then had sex with wife, producing children. Presumably the author's intention was that he had already married his sister and took her with him when he fled.