The black mark is just toning (I guess?). That should have little to no impact on the grade.
Anyway, it should have made MS in my estimation. ICCS is tougher on NL coins than they are on Canadian coins. If that was a Cdn coin the grading result would be different. It's a terrible grading imo. Where is the wear that would bring it down to AU. A simple grade is not enough! All grading service should have a note or description explaining the grade given.