Compared to how many emails he sends in total, it is barely even a few. By and large, you will not find a more friendly maintainer. If you keep ignoring him while trying to get something into his project, he will get rude.

And this is the funny thing about it. Even the people he "explodes" on usually get a lot of friendly "stop" messages from him well before any inflammatory message comes out. Only real exceptions I can think of is that he will meet an insult with an insult. Which, ironically, can go a decent way to making everyone else feel safer in the environment.

Edit to add: I do want to quickly add that as much praise as I can offer Linus in this regard, Knuth really is on another level. I do not intend to compare them.