Each and every time that the old man fought against Adam or taught him something new, he was pleasantly surprised by how quickly Adam was able to learn and grasp what he was trying to teach him.
He was the perfect student that seemed loyal and would never complain, and knowing that, the old man was beginning to warm up to him. However, that scared him and after being betrayed, he didn't ever want to feel vulnerable and allow himself to be stabbed in the back.
Because of that, he was still subconsciously wary of Adam and he wasn't yet confident in Adam's loyalty to teach him something that was valuable and dear to him.
However, he was still willing to strengthen Adam's foundations and teach him the fundamentals while testing his character and potential along the way.
"There is no need for you to return to your home, there is a lake deeper into the forest that is surrounded by small mountains and trees, so there shouldn't be anybody there," said his master.