Yeah, that's what I was suspecting.

I ended up leaning towards "download" being used in the boomer way of meaning any data transfer, whatever the direction, which in this case would more specifically be called an "upload". And that "online" was being used to mean "using a website", even though the local processing is offline.

The alternative fit to the description I had considered was a website you could give an URL, so it retrieves the zip file and allows you to inspect it remotely, and maybe just download some of the contained files, so it deals with the risk and bandwidth issues for you. That would be a different kind of useful, though it'd only be a few days before someone uses it for malign purposes and gets the site operator a no-knock visit from the fuzz, so that seemed much less likely.

I can see a use for an app that can be used where they can't be installed, though.