there are different classes of misdemeanors but what does it really mean to have an unclassified misdemeanor?

Answer 1

Not all jurisdictions classify misdemeanors.

The general point of classification is to have a single sentencing statute (or single list), and statutory entry for each misdemeanor defines the elements, but uses the class to refer back to that sentencing list.

For states that don't do classifications (and US federal), each crime has its own defined sentence as part of the statute.

Even if the jurisdiction does classify most crimes, there may still be some that include their own sentence limits -- which since they are not part of a class, would make them unclassified.