Their connection doesn't look... convincing? They didn't spend enough time together with the MC to even become distant acquaintances, not to mention friends. They traveled together for a few days and that's all. The way they act like best buddies is weird, especially for a clan well known for poison martial arts.
I would understand if the MC was surviving in the forest alongside with them, while building organic friendship, but he was basically training on his own all the time.