This is a great statistics lesson. All that's happening here is that the Erlang number is more volatile than the other numbers because the absolute number of samples is so low for Erlang. See the following, much better graph:

http://www.indeed.com/jobtrends?q=lisp%2C+haskell%2C+erlang

As you can see, there are literally three times more job ads that mention Lisp than Erlang, and 1.5 times more Haskell job ads, little did I know. And Erlang went from 0.0005% to 0.002%, which is indeed a very high growth rate -- but what happened here is that we went from 10 or 20 or Erlang ads to 80 or 100. [1] With numbers that small, no wonder the fluctuations are so large.

Of course, given that I wouldn't dream of hiring an Erlang programmer by posting an online job ad, I doubt these numbers are worth much anyway. But, to the extent that they are worth something, they're not bad news for Erlang fans.

[1] Indeed.com claims to index "millions of jobs". 0.0005% of two million is 10.