His master may be a fake, but the teaching he said to him weren't, the training as well.
He may not realize but the things he told him to master, the thing about magic and sword as one, and the training of his senses and the way he should view the path of the sword, they all had great impact on him.
He himself may be a phony, but his disciple was surely not.
Therefore I'd say he did his job as a master well thanks to these results.