Is the “Unclassified” traffic referring to network traffic that cannot be identified based on the signatures?

Correct. Unclassified Traffic are those that has not been classified by Sinefa Network Layer7 classification engine.  Sinefa provides the port numbers if you hover over "Unclassified" in the Sinefa Dashbboard and customers can investigate further.

If those applications are legit and are specific for this customer, customer can also add these custom applications to the list based on the port numbers discovered.