Where did you get "almost certainly" from that article?
Well, there's this:
"Almost certainly" may be incorrect, but it does appear fairly likely given this.
Not here in Austria, where both the telephone polling and the internet polling shows roughly the same results for the FPÖ (online pollster meinungsraum.at had the FPÖ at 19% in the final poll for the 2013 federal election and the telephone pollsters had them at 20-21%. The FPÖ then got 20.5%).
But in the 1990s, Austrian pollsters terribly underestimated the FPÖ and the party always polled much higher on election day.
Since 2000 though, pollsters refined their methods and compensated the "shy-FPÖ-vote" and now they are even overestimating the FPÖ's vote sometimes (but not by a lot). Of course, much higher turnout in Austria than in the US also helps with the poll's accuracy.