Looking at their raw data, it looks like there was a total of 718 respondents (https://docs.google.com/spreadsheets/d/1Km9bsx0SWPDiOPMYvrem...).

Large enough sample to be ultra conclusive? Not really, but I think it gives you a taste for the data and it's unlikely that tech interns /do/ make more than most, but it's not really surprising.