Hi there,
WP Offload Media Support Team here, Thanks for reaching out with your query we would be happy to assist!
This is the expected behavior of that tool/setting. Only the files are removed, but the Media Library database records are retained. The plugin works closely with the Media Library records in the database.
https://deliciousbrains.com/wp-offload-media/doc/developer-guide/#automatic-offload
The file you see on the Media Library is due to the Media Library records found on your database.
Rest-assured, if you enabled Remove Local Media, the files should automatically be removed from server after being offloaded. You can verify this by checking your “wp-content/uploads” directory and checking whether the file you uploaded via your WordPress Media Library is still there.