He's not really a project manager for Linux, to clarify what was said above; he is the coordinator of development of the Linux kernel, the very heart of the GNU/Linux operating system. For what it's worth, this is the largest software project that has ever existed by several orders of magnitude; it's seen hundreds of changes to its source code per day for the past decade. This is not a small project, and managing it is not a figurehead role.

Also, please note that Linus' way of interacting with other people online is, at least according to him, a calculated strategy which is part of his management style. For more details on this, it's instructive to read over his brief and entertaining (to me, anyway) document on kernel management style. [1] Here, he says revealingly that he doesn't think it's possible to be polite all the time, so it's better to try to criticize everyone equally "so evenly that nobody really ends up feeling like they get unfairly targeted. Make it inventive enough, and they might even be amused." He also says that politeness usually masks honesty, and that he doesn't think anybody is likely to trust you if you spend a lot of time being polite.

I think a lot of this has to do with his character, but it's worth noting that he is not oblivious to the way he comes off. He believes he's come up with an effective strategy for managing the incredibly large and important project he's in charge of, and it's hard to argue that it hasn't had some spectacular results. Even if you disagree with how he approaches it - and I emphatically would not approach any management job the way he does - you have to admit that he's conscious of what he's doing and he believes it has a purpose.

[1] http://lwn.net/Articles/105375/