Thank you for reporting a bug to Unity.
When reproducing the bug, I can see that the platform specific compression settings for Mac, Windows + Linux is set to RGB Compressed DXT1, so Project Auditor seems to be reporting the correct thing.
So even though the default compression in the Texture Importer UI is set to None, it is overridden by the platform. If you analyze a different platform, you should get a result that corresponds to the compression that platform will use.