http://www.thefreedictionary.com/judicial+activism
There is no conceivable way that the mere act of reconsidering previous precedent and not following it is "judicial activism" under the definition. The ruling could very well be judicial activism, but not because the court doesn't follow precedent.
Black's Law Dictionary:
A philosophy of judicial decision-making whereby judges allow their personal views about public policy, among other factors, to guide their decisions, usu. with the suggestion that adherents of this philosophy tend to find constitutional violations and are willing to ignore precedent."