I figured out the answers by myself.
Just in case anyone is interested, here are what each criteriatype value means in the mdl_course_completion_criteria table:
| 1 | enabled condition "Condition: Manual self completion" |
| 2 | enabled condition "Condition: Date" |
| 4 | enabled condition "Condition: Activity completion" |
| 5 | enabled condition "Condition: Enrollment duration" |
| 6 | enabled condition "Condition: Course grade" |
| 7 | enabled condition "Condition: Manual completion by others" |
| 8 | enabled "Condition: Completion of other courses" |