Yes, you are just fetching a bunch of objects into the collection of School.
The collection 'Tutors' in school, is the facility to fetch the tutors related to the school object.
If you want to filter these further, you have to use the GetMulti() method of a new TutorCollection object, and specify the school's PK as well, or do as you do now and specify the school's PK as well. This last option seems odd, however the logic in place to fetch the Tutors is just fetching all tutors for a given school, namely the school containing the tutors collection to fetch