No, it isn't using the app store. A company rents an enterprise certificate from Apple for $299/year. The company can then sign as many apps as they want using

No, it isn't using the app store. A company rents an enterprise certificate from Apple for $299/year. The company can then sign as many apps as they want using that certificate, and distribute the apps through MDM, itms-services links or manually using IPA files installed with iTunes. Apple can remotely revoke these certificates. However, Apple does not know which apps are being signed, unless they are informed through (in this case) the media.