I think the statement that his answers may seem impolite is more a commentary on many people's inability to distinguish terseness from impoliteness. It's not saying that he's rude.
Maybe. I have indeed seen cases where nice but busy and terse people were incorrectly interpreted as rude. But from what I've read about Stallman, I'm more inclined to think he's kind of a jerk. Often, people who are busy, and especially people who are passionate like Stallman, tend to look down on other who don't share their passion.
This isn't the end of the world. I'm kind of a jerk.
many people's inability to distinguish terseness from impoliteness
That's exactly it, though. Politeness and terseness are often diametrically opposed in our society, and since there is no standard of politeness outside what society finds to be "polite", I'm not sure how you can say many people have an inability to distinguish.
If you email a long question to someone and they respond with "No.", many people would find this to be impolite or downright rude. It might be the most efficient thing and the hacker-type might think it's OK, but if most people think it's impolite, it is.
That's because if it's a long question it generally requires a longish reply to explain to the other person why the answer is "no". Saying simply "no" strongly suggests that the other person's understanding is not worth your time, or that they should accept your answer without understanding it because you are higher status.
