It is interesting to read the opinions offered by the Court.  I think that the case is an example of activism because it represents the court using its power to right a perceived wrong present in the law passed by Congress.  Justice Roberts actually argued that the decision of the court helps to keep principles of judicial restraint in tact.  I am in no way qualified to out think a Supreme Court Justice, so I would advise you to read over the decisions offered by the Court and assess for yourself how the justices interpret the analysis of judicial restraint or activism.  It does seem like the Justices sought to remedy some type of error they saw in the law, which fits the definition of activism, but I pause again to stress the need to read the decision and analyze how the justices address the issue of activism and restraint in their own thoughts.

This is more consistent with judicial activism, in my opinion.

The doctrine of judicial restraint argues that judges should defer to the elected branches of government unless it is crystal clear that the Constitution invalidates a particular law that has been passed by the elected branches.

In this case, the Supreme Court has found that a law passed by Congress breaches the First Amendment even though it is not completely obvious that it does so.

Because the decision overturns a law that does not clearly violate the Constitution, it is not really consistent with the idea of judicial restraint.