Teacher sections are different from student sections.
A teacher can be the default teacher of a section (modified in the Section Details) and as such, all periods of the section will be visible to them.
A teacher can also be a secondary teacher. This is set in a Section Schedule within each entry of the schedule.
Multiple teachers can be assigned to different periods of a section (co-teaching)
Warning: You can also add sections to a teacher’s schedule the same way you can do it for students. This will not make them teachers of these sections, but appear as students and they will not be able to publish to them.