It all depends what you mean by "Winzip files". It's better to talk about the actual file extension whatever it is.
Winzip can open ISO files so you can see the contents. If your friend has installed WinZIP with default options, very likely it has become associated with ISO files as well as the .zip files which you think of as "winzip files".
If your friend has Windows Explorer hiding known file extensions, very likely an ISO file will just show up as a "Winzip file" just like a .zip file would, with the WinZIP icon, and he won't be able to see what type the file actually is. Except by hovering over the file name and viewing the tooltip that should show up.
So tell him not to worry.
Many archive programs such as WinZIP, WinRAR, etc can open some other common file types, including ISO files, as well as the ones you might think of as as their "native" file formats.
If WinRAR is asociated with them, Windows calls .zip files "WinRAR files" for example.
Tell your friend to turn on file extensions then all will become clear.
