No, they are correctly installed, they should be in /usr/local/qwt-6.0.0-rc5/lib. But this directory is not in your PATH, therefore the library cannot be loaded on startup of the application. One possibilty is to add this directory to your PATH variable, or you make a softlink:

sudo ln -s /usr/local/qwt-6.0.0-rc5/lib/qwt.framework/qwt /usr/lib/qwt