Did you debug the issue? You can post the findings in the support forum at the bottom of the plug-in page https://moodle.org/plugins/report_coursesize itself or post them in the forum General plugins https://moodle.org/mod/forum/view.php?id=44.
4 TB is a terrible size for moodledata. Did you investigate whether all that is genuine/legitimate? Either way I don't think the plug-in scans moodledata. The file sizes are stored in the database.