This is native libzstd build as nuget package for .NET ecosystem.
It includes windows and linux build, which:
Windows build came from https://github.com/facebook/zstd/releases you can match the sha256 from there with the lib shipped here for the build version.
Linux build came from https://deb.debian.org/debian/pool/main/libz/libzstd you can match the sha256 from there with the lib shipped here for the build version.