What specific version of OS X, or macOS are you currently running? menu : About This Mac? If that folder of Numbers content is on your Mac, rename the folder to test.numbers.
Sign into iCloud Drive, and use Numbers for iCloud to open that test.numbers package folder. If that does not work, then right-click on that test.numbers folder and choose Compress "test.numbers". Rename test.numbers.zip to foo.numbers. Then try again to open foo.numbers with Numbers for iCloud.
If Numbers for iCloud cannot open foo.numbers, then download the free LibreOffice v6.1.3+ (if using OS X 10.9 or later). Once installed, right-click on the Applications/LibreOffice icon, and choose Open. Click Open on the following dialog, and then attempt to open the foo.numbers document with LibreOffice Calc. It cannot open the package folder format named test.numbers.
If Numbers for iCloud, and LibreOffice Calc cannot open the foo.numbers document, then you are done, with no recovery possible.
Both double-clicking a Numbers document on Windows, or attempting to open with Google Docs will destroy the document.