Completing and submitting an assessment does not mean the assessment has been published to students.
When creating a course assignment, the Publish Assessments checkbox is selected by default under the Assessment setting on the Assignment Details page.
This setting allows a student to receive the assessment results instantly after an assessor completes and submits the assessment. You are able to uncheck the Publish Assessments setting on the Assignment Details page so that assessment results are not released to students until all students in the class are assessed (i.e., all are in the Completed green column). Once all students in the class are assessed, the Publish Assessments button on the Submissions & Grades tab is enabled to release all of the assessment results at once.
Note: If you would like to keep the assessments hidden from students don't click the Publish Assessments button.