Actually, I have a pretty serious issue with all of this.
RMS was working on GNU for a while, around the same time the BSD camp was writing what essentially was an open source replacement for AT&T's Unix. The BSD camp didn't call it "open source", but for all intents and purposes it was open source. (GNU was announced 1983, BSD's first release was in 1978).
Linus came along and went "Gee, it'd be nice to have a free version of Unix I could use at home! Oh look, BSD!" Then Linus saw the law suit taking place between AT&T and BSD, and thought "well, no sense in bothering with BSD, I don't know if it'll still be here in six months". Then he noticed GNU and thought "well, if only I had a *kernel* to go with this GNU operating system." And Linux was born.
Now, did "GNU/Linux" lift off because of GNU, or because of Linus? It's *really* hard to say...but looking at GNU's kernel choices, I'd say Linus had a great deal to do with it...because it's *really* difficult to run applications on top of a kernel that doesn't work (see question #13 here:
http://www.redditblog.com/2010/07/rms-ama.html).
This can be attributed to a law suit by a massive US corporation who cared nothing of freedom (user *or* software).
I'm willing to bet, though, that if Linus had put his skills to use in BSD, the open source landscape wouldn't be incredibly different from what it is today...Stallman or not.