In this particular case, the download was corrupted. Errors can happen during the download process and the larger the file is the more chances it has to be corrupted. This can happen during the download itself or as the file is being written to the drive.
To resolve this, you need to verify your download. The directions to do so are located on the Elementary OS Installation page. This will vary depending on your operating system - and the checksum will change as the distro changes. So, be sure to check there and ensure your downloaded ISO is in fact bit-for-bit correct.
If you want to have your download automatically verified, you can actually use a Torrent client to download the ISO. You do this by clicking on the magnet link in the download window.
For visual reference, this is what it currently looks like:
Files downloaded with a torrent client (using the magnet link) will automatically verify the integrity. The added bonus is that you can keep your torrent client open and help the project by saving the download site(s) some bandwidth.