In my opinion, in the software world, there is a large number of people who are very convinced of their own correctness. When they do something wrong or are simply mistaken, a gentle correction doesn't work. Linus is probably used to dealing with these people. I'm not saying the person he was replying to was necessarily doing that, but after a while you have an automatic response.
The beauty and horror of OSS is that anyone can contribute. Having someone scream "WTF are you doing???" every once in a while isn't a bad thing. It's not nice to hear that being directed at you, but sometimes in life it is necessary.
Too bad there was no around to do that to Linus; maybe he'd finally realize that being an asshole is generally not a correct response.