The file system hierarchy standard (
http://www.pathname.com/fhs/pub/fhs-2.3.html) says that /usr/lib contains libs for user programs, and /usr/lib<qual> contains libs in
another format, including a different architecture.
Without knowing it, I assume that Ubuntu symlinks /usr/lib to /usr/lib64. So when you tried to copy files, it did not work.
So general rule is: /usr/lib always contains native libraries, but might be a symlink so that some file operations have to be treated differently.
As someone else said: Build SFML yourself and let CMake handle the installation. It will take such things into account.