I think while when one says open source, Linux quickly comes to mind, in its true nature, open source goes far far beyond just Linux. There are open source applications that run on a variety of platforms, like Macintosh, and even windows.
Open source is such a vague broad term referring to programs for which the source code is publically available. Just because tow programs have publically available source code doesn't mean that whatever you can do with one you can do with the other. People who make open source projects have different opinions on what they want people to be able to do with their code, which is why there are so many different licences. BSD licence is very open while GPL requires someone who builds something using GPLed software to make what they build open too.
While its understandable why open-source and Linux are so closely related, this is not an accurate assessment of the situation, and I think people should take care not to confuse this.
V