Yes, that's right. Silly of him to do so (and of me not noticing he did).
Note that all body hair is suitable for testing, not only scalp hair. Quite apart from the fact that showing up with a totally shaven body might give them the idea of locking you up for a few months to let hair regrow in jail. Plus adding a charge of obstructing the course of justice.
I've read 3 months is the usual time-span for detection in hair, except in case of heavy usage where detection can go back as far as 2 years. The exact time of consumption cannot be pinpointed however, owing to the fact that metabolites travel along the hair with time. So althoug you can fine-tune your lie about when it happened, it is seldom a good idea to deny consumption except a light consumption going more than 3 months back.