the way i read it 

The presence of zstd-jni in the Databricks Runtime 7.3 LTS release notes primarily indicates that the native JNI library for zstd compression is included in that runtime version. However, this does not equate to full official support for using zstd compression as the Parquet codec within the Databricks platform.

While Apache Spark 3.0.0 and above introduced zstd compression support, Databricks Runtime 7.3 LTS (which includes Spark 3.0.1) does not officially enable or support writing or reading Parquet files compressed with zstd. The Parquet compression codec support for zstd was formally introduced and supported starting from Databricks Runtime 8.0.

Therefore, despite the inclusion of the zstd-jni library in DBR 7.3 LTS (see release notes — https://docs.databricks.com/aws/en/archive/runtime-release-notes/7.3lts), you should not rely on DBR 7.3 LTS for production workloads involving zstd compressed Parquet files, as this can lead to compatibility issues or failures.

For official confirmation and compatibility details, consult the Databricks Runtime release notes:
https://docs.databricks.com/aws/en/release-notes/runtime/