No; open source encompasses copyleft, which broadly requires derivative works to be under the same or similar license, and permissive licenses, which generally

No; open source encompasses copyleft, which broadly requires derivative works to be under the same or similar license, and permissive licenses, which generally don't care and are happy to let you incorporate the code in differently licensed derivatives up to and including producing completely proprietary programs using permissively licensed open source code. Darwin largely uses permissive license code, in particular from the BSDs, which means that it's under very little obligation to share. (IANAL and this is somewhat oversimplified, but that's the gist)