Board.KolibriOS.org

I mostly agree with his answer, but what was the point of your question?
"Don't need to learn" doesn't mean "forbidden to learn"
And this is a hobby OS, so we write it in the language we want

You should ask Linus Torvalds about that - why are you asking us? How would we know what Linus Torvalds thinks?
You don't have to write in Assembly to contribute to KolibriOS - we support many other languages: http://diamond.kolibrios.org/hll/hll_eng.htm But of course Assembly is the preferred language, and it's mandatory for kernel.
The Offtopic forum has limited edit capabilities for a reason - the messages that are here should better not exist at all, but because we are so kind, we are letting them stay, although limit the changes in them.

C is the choice to go for fast development and he knows that writing in C helps to multidevelop things, but still assembler is in linux. It is more or less a best case suggestion from him I guess!