The matrix can show 100% completion if all configured traceability checks are fulfilled, even if some items are present as dangling or unrelated, as long as they do not violate any enforced traceability rules - depending on configured checks. 

If all default trace checks in the traceability module are 100%, the project will be viewed as having full traceability. While relationships are bidirectional in the data model, default traceability checks focus on downstream enforcement per MAN-07 and the V-model. 

Checks within your traceability module can be configured. For details, please see trace configuration documentation here.