This is a bug but support suggests this be posted as an idea to raise awareness. https://support.esri.com/en-us/bug/status-dashboard-for-credits-shows-combined-size-in-ite-bug-000141394
AGO Org status Dashboard for credits shows combined size in item details summary for feature and feature attachments. When viewing items through the feature data store in credit status dashboard, hosted feature services are listed by size where table export is available. In looking at the items sorted by size and table export, the size values are incorrect. Hosted feature service size is combined with feature attachment size. This results in total size and assumed credit burn of .24 credits per mb per month to be significantly inflated. This behavior is also observed when pulling org items through the ArcGIS Python API.
