GitHub Tag vs Release and "importability"

I apologize for the awkwardness of my Title. The context of this question is utilizing packages whose source code lives in GitHub.

I understand the difference between a Tag and a Release. But I do not understand how either affect “importability”… meaning, my ability to import that package and use that version in my code.

This package pillow has various releases and I am able to import that package in my own app. This package flake8 has only Tags and NO Releases yet I can also import that package into my own app. How is this possible? Are there Tags which are impossible to utilize by my application or are they ALL available? Is there a difference between a git tag and a package tag? My assumption was that a Release was a Tag that a package was making available for consuming.

Would appreciate any help.