Prior to the referendum poll numbers were saying the exact opposite of what the election results came out to be. The EU thought they could scare Greek pensioners and gov workers into submission, but apparently that's not the case. Tsipras still wants a deal though, just one with less onerous terms. An outright Greek default on the debt would be very damaging to the EU financial system, so this game of chicken will continue, only now with Tsipras in a somewhat stronger position.
And if it turns out that the EU is willing to do that, then I guess the Greeks did indeed make a good move.
At first glance, it seems absurd that the EU would do that, but then again, they are Socialists at heart, and making irrational, and economically unwise decisions is what they do!