It must be frustrating for RMS that his dream of a free software OS was realised in the form of "Linux", but I'm pretty sure that one of the freedoms that flow

It must be frustrating for RMS that his dream of a free software OS was realised in the form of "Linux", but I'm pretty sure that one of the freedoms that flow from a free software license like the GPL is the freedom to call the software whatever you like. Thus I'm free to distribute an operating system that contains a tonne of GNU software and then put the name Linux on it, and the license allows me to do that. If RMS had realised that the name was so important, maybe he would have added a restrictive naming clause to the GPL.