I’m confused. How are you defining “download” and “online” here?

The website suggests that the server holds the files and does the extraction:

Extract and Explore compressed files online [emphasis mine]

which fits with the github claim of:

to view and extract zip files online without downloading them

but the website also states that:

nothing leave your browser

which suggests that the server has nothing to do with it, and you do actually download the zip files first.

What am I missing?