Yes, putting such temp folders/files on the desktop can be unnerving. And I'm cautious about telling someone what they can and can't delete!
But I think you are right that these are the setup files, and can be deleted. Since some of thenm are large and migt be needed for reinstallations, I usually save them to a different directory to begin with, or move them when the installation is complete.
This second step that provides the buttons etc in the library does not have an installre. You just extract the files and put them, or move them, to the correct location. If you are getting something that looks like an installer, ask us about the file name here.