Who is hosting the remote disc when reinstalling OS from remote disc I have a used mac book pro and have to reinstall the OS from remote disc. My question is: is the remote disc in this case (OS install) hosted by Apple or is it hosted by some other users' laptops?
Remote Disk is a method for sharing another user's CD/DVD drive over your local network, if your own Mac doesn't have an optical drive. It's not a method for installing an OS onto a blank Mac. 

For that you would use Internet Recovery to reinstall your OS from scratch;
hold  Cmd ⌘   Opt ⌥   R   at the boot chimes.
This will load the image directly from Apple.  

See Apple KB: How to reinstall macOS