I took this to mean that the average startup employee is in their late twenties, and he is somewhat older than that
Sure I know other languages: Shell Scripting, Perl, HTML/CSS/JS, Groovy, SQL, C#, etc, but 80 percent of the code I write is in Java. I'm at a Java shop and have golden handcuffs. It's Java or bust for me.
The languages in your list are:
* declarative: HTML, CSS, Groovy (for Gradle), SQL
* scripting: Shell, Perl, JS, Groovy (for testing)
* Java-clones: C#
I found it difficult to pick up Clojure and Haskell "in a few days" when all I had was experience in those types of languages. In fact, mastering each of those languages requires a change in thinking that can only occur over a much longer time.
I did do some non trivial work in Lisp in a graduate class, but its not the same as using it all day. I don't believe I would seek out an opportunity where a Lisp dialect was the programming language of choice, anyway...
(I found ML to be easier to work with than Lisp. I guess it's technically not a pure functional language though).
I do agree with you that someone who claims to pick up new languages in a week should already have picked up a few languages. The grandparent says they only do the _majority_ of their programming in Java, so perhaps they have that covered. I'd love to know what the other languages they've chosen are, and their dissimilarity to Java.
I don't know how to evaluate their claim that they're a really_good programmer, given that it's a throwaway account. But then, given the data of this article, I guess no one does.
On the one hand, you're right, you can't learn everything. On the other, to be able to realistically claim that you can pick up new languages quickly, you should already know three or four different kinds of languages. If all you know is Java, you probably are farther away than you think from picking up a very different language like Ruby. I would encourage you to do some study on the side. Your late twenties is far too early to let yourself get pigeonholed.