Whether or not you see his behavior as polite, I guess, is a matter of how you read people and the context of the situation. That said, he did literally admit he was being "terse". I think it was counterproductive at best and rather mean at worst.
As for whether it really is "difficult", one has to ask for whom? For someone that is intimately familiar with C++, DirectX, internationalization, the nature of production-grade terminal shell applications and all their features and requirements?
And even if it is "easy", so what? It just means Microsoft missed something and perhaps were kind of embarrassed, that's totally human, it happens. It's not so nice when this stuff is very public with harsh judgement all around.
This all rubs me the wrong way. I have found the Microsoft folks to be very helpful and generous with their attention on Github Issues. They've helped me and many others out, it has been genuinely refreshing. What this guy did might discourage participation and make folks more defensive to avoid losing face in a big public way over a mistake or silly gotch-ya.