One of the default features in Canvas is for grade distrubtions to be present for students. This allows students to see the highest/lowest grades on a particular assignment, as well as how the grades distributed based on quartiles (25% of students received a grade between X and Y).
If you do not want students to see these distributions, you are able to turn them off with the following:
1) Go to Settings on your course navigation
2) Under the Course Details tab, scroll to the bottom and click "More Options"
3) Check the box that says "Hide Grade Distribution graphs from students"
