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I just tried downloading it from a Windows and a macOS computer using Firefox and Chrome. In all cases I can test and extract the archive both with Info-ZIP's unzip (that's what Linux servers use) and 7-Zip. I also tried with the built-in ZIP archive support in Windows File Explorer and Finder. I can extract the archive just fine.

Based on the message you are receiving, something is appending data to the file you are downloading. That something can either be malware that has found its way on your computer, a proxy server used by your company / school / organization (assuming you're not downloading from your commercial broadband or cellular Internet connection) or a proxy your ISP is using. I have seen examples of all of the above. Malware is self-explanatory: they can interject themselves on the operating system's network layer and append malicious Javascript (or ads, if they're desperately naive) to the pages you are downloading. I've even seen antivirus / Internet security software following a similar approach, adding Javascript which is supposed to protect you (but ends up simply breaking everything). The latter two cases, i.e. a proxy used by the network provider, is a bit more complicated. Organizations may choose to add tracking Javascript to all downloaded content for regulatory, compliance or plain old snooping reasons. ISPs, especially low cost or free ones, may choose to inject ads in pages to pay the bills.

At this point I'd recommend trying to use a live Linux USB stick, i.e. boot your computer through a USB stick that has a Linux distribution, such as Ubuntu Linux. Use it when connected to the network through a different ISP, ideally a consumer ISP, not a school or other organization. If you still get a problem I'd recommend using a different unarchiver to extract the ZIP file. I've tried the built-in features in Windows and macOS, as I said, as well as 7-Zip. You can even use our Akeeba eXtract Wizard (desktop) or Akeeba Kickstart (web) to extract that ZIP archive.