If your backup was downloaded as a tar or a tgz file using the compression of the script you made the backup with; yes. If you have a .sql file, it is not likely, and is more likely that the script you used to generate the backup choked and fed you what it had recieved.
Also, ZIP is a way differant algoritm than Tar or Global Zip; or Tar and Global Zip togethre.
And it's quite odd that the file would change size like that, possibly a bug or something :shrug: I don't use scripts to make backups as you end up with either many files, lots of lag, or things that just doont' work properly
