老师 means "Teacher". In english Schools you dont usually refeer to you teacher, lets say Li, as "Teacher Li", but as "Mr. Li".
In chinese, like in english, its really comon to refeer to someone by its profession, "Doctor Li", "Detective Li"... But I think that "Teacher" is one profession that does not feel natural to call like that, so probably the translator decided to use a more natural "Mr".
In chinese, like in english, its really comon to refeer to someone by its profession, "Doctor Li", "Detective Li"... But I think that "Teacher" is one profession that does not feel natural to call like that, so probably the translator decided to use a more natural "Mr".