The argument is "You must master javascript". If other languages compile to javascript - then you needn't master javascript, you can master those other languages.
So no, this does not just support this argument. There are other languages to learn.
When Steve wrote this article, his point was Javascript or anything that creates Javascript. Or actually, we don't even really care about Javascript, just the portability and qualities we get from it and its derivatives or offshoots. Another suitable title would be "Server side only thinking is dead".
