1. He is expected to comment or answer questions like this ALL THE TIME. People only have so much patience. Don't believe me? Go to a poor country as a tourist and see how quickly your tone changes when poor people constantly approach you. Or ask a good looking young woman how it is for her when she goes out.
2. Life is tough, deal with it. This expectation that everything has to be nice and safe and friendly all the time lead, amongst other things, to the NSA mess we have right now, as Schneier pointed out recently [1]. We want EVEN MORE safety. And you want everyone to be nice. Well, what do you prefer? Some tough love from a guy like Linus, or friendly words that neither help you improve your knowledge (in this case) or, worse, someone that pretends that you are doing alright when, in fact, you aren't.
3. If this kind of communication helps to weed out people that are incompetent more successfully than other methods, then isn't it acceptable?
Finally, and this is a little bit of an unnecessary tounge in cheek comment, I recommend you go watch an old Sergio Leone western. And then reflect what a guy like Clint Eastwood would have to say about your comment. Not, much, I suppose. ;)
[1] https://www.schneier.com/blog/archives/2013/09/our_newfound_fe.html