Here's the short answer: Our Citation Tracker tool is a specialized tool for finding and filtering citations, whereas our Google My Business tool reports a broader set of metrics and doesn’t use such a sophisticated system for finding and filtering citations.
If you want to find out more about how we find and filter citations, please read this FAQ
And here's the slightly longer answer: Our Google My Business reports are primarily focused on analyzing Google My Business data while giving you a "lite" view of citations at the same time.
Google My Business reports simply use Google to identify listings, and perform a real-time look-up of citations each time the report runs. Citation Tracker, on the other hand, has a far more complex and dedicated process for identifying citations that uses an extended list of searches, APIs, and filters. Citation Tracker also stores and reuses citations from one report run to the next, rather than performing a fresh citation look-up each time.