He would still need an installer drive to have the macOS Utilities necessary to restore from the internet to the best of my knowledge. So the internet download takes the place of what was once a set of DVD-ROM discs that contained the entire OS, but you still need the installer to make it go.A late 2014 Mac should be able to reload the OS over the internet, iirc. Maybe Google "how to restore MacOS" for some tips.
The installer drive can be on as little as a 16GB thumb drive, as it doesn't contain the entire OS itself, just the utilities necessary to install it from the internet (unless something has changed since the last time I did it just a few short years ago).
The problem is I'm not aware of a way to create the installer boot drive without another Mac, I guess it's possible to use a Windows or Linux machine to do that, but I've never heard of anyone actually having done that.
EDIT: apparently it can be done with Windows 10/11 and software called TransMac: