smb.conf(5).gz is probably a gzipped manual page, not a gzipped tar archive.
gzip is a compression algorithm that can be applied to any type of file; tar is a file archiving format that lets you put several files into one but doesn't compress them.
Assuming it is a manual page, you can view it with the man command in a terminal.
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You can always use gunzip to uncompress .gz files, and file to guess what kind of file it is.
Hope that helps!