It's one of the most comprehensive surveys to date. Meanwhile, the job numbers can relate to many factors. For example, there could be more turn around for Scala jobs.
"Welcome to the largest survey ever of Java developers ... The survey was conducted by publishing its availability to the Java community at large (via social media primarily), to Java User Groups around the world, including the Virtual JUG, and to subscribers of Java Magazine, the Java bimonthly publication from Oracle Corp."
So the sample is heavily biased and doesn't include the population of JVM users who have never touched Java.
That's very likely the case, but presumably you'd get an even sampling from the users of other languages. It would be interesting to see some more surveys focusing on the larger JVM ecosystem though.
