Resource Manager uses the ResourceUpdateSummary table as the source for this value. If you run the following query at different times of the day and compare the top few data classes with the date and time stamp that is being displayed in Resource Manager, you will find the data class that is being used at that moment.
SELECT vc.[Name] AS Resource,dc.[Name] AS [Table],rus.CreatedDate,rus.ModifiedDate
FROM ResourceUpdateSummary rus
JOIN vComputer vc
ON vc.Guid = rus.ResourceGuid
JOIN DataClass dc
ON dc.Guid = rus.InventoryClassGuid
WHERE vc.[Name] = '<machine name>'
ORDER BY rus.ModifiedDate DESC