That advice contradicts the diagnosis of a Grade 1 ACL tear. i.e. one that does not require surgery. If you have has a full (Grade 3) rupture and want to play sport then a reconstruction would be my suggestion. It is early days and to be honest if it is a grade 1 then you can't tell how that has affected the feedback/feed-forward mechanisms that the ACL provides to the brain during movement. Only then will you know how stable the knee is and what can be combated with conservative management. In either respect any conservative rehab you do would be the same you'd need to do post surgery so all time spent doing it would benefit a later surgical intervention.