Is this about a refusal to learn new things, though? He does, after all, point out towards the end that good programmers use multiple languages - so whilst a refusal to learn new things is a bad thing, isn't a bit of prudence in how to budget your time a good thing?

True he does qualify his initial assertion near the end of the post by saying that to be marketable you need to know multiple languages. I guess what bothers me about this piece is the sense I get that the author is writing from the perspective of optimizing ones personal profit. He is basically saying the only reason to learn multiple languages is for competitiveness in the job market and even then you should learn as few as you can get away with as well as possible.

That sounds like the argument of a technology major to me rather than a comp. sci or engineer. He totally ignores the fact that many languages are based around the same core principles and if you know those well learning a language is like learning a new word from the dictionary it just happens naturally when it needs to be done.

You misread the article. He's not arguing against learning new things. He's arguing against learning the specific new things you want him to; he'd rather learn business or security.