Results were gathered in August 2014 by Cameron Moll. The sample size (471) is rather small and therefore should not be construed as indicative nor representative of the entire HN audience.
The sample size doesn't indicate how representative a sample is, the polling method does. In this case, it's almost certainly not representative - internet polls rarely are. But even a sample of 5000 wouldn't be representative.
You may be thinking of statistical significance. 471 is actually often a pretty good sample size, you would e.g. need <100 responses to have a fairly significant estimate of the mean salary of HNers (assuming a representative sample).
