Safari opens zip files

Open Safari and in the menu bar of your computer, and go to
“Safari” > “Preferences” > “General”
Find the option that says “Open ‘safe’ files after downloading” and uncheck it.

This video shows the process:

Then, re-download the original zip file and it should not be unzipped.

Select a group of files on your computer, and use the right-click of your mouse or trackpad to choose “Compress” from the options.
Files should be compressed into a file called Archive.zip and you can rename this zip file if necessary.

This video shows the process: