The scenario from the post is acceptable only because it is running on a Mac Mini running Linux. If it were running on any non-Apple hardware it would not be permissible -- even if he bought an Mac Mini and never used to attempt to "buy a seat", because the Apple license states:

"The grants set forth in this License do not permit you to, and you agree not to, install, use or run the Apple Software on any non-Apple-branded computer, or to enable others to do so."