Library author
The developer has published a reusable piece of code that other developers download and build their own projects on.
What it tells you about a developer
Library authors design for other developers, which forces clean interfaces, documentation, versioning, and support. That is API design and platform thinking, and it is valuable for senior and staff roles.
Package registries like npm and PyPI work as app stores for code building blocks. Publishing a package with real download numbers means other developers chose this person's code as a foundation. It is a sparse badge: most developers never publish one, so its presence is meaningful and its absence carries nothing.