No. Judicial activism means misrepresenting the Constitution, not defying precedent.
And that "precedent" was based on what? It was based on a previous intepretation of the Constitution.
Defying precedent, therefore, is defying a previous interpretation. Now, if that previous interpretation were "wrong", then isn't judicial activism actually correcting the wrong, resulting in a true (or truer) representation of the Constitution?
The bottom line? Yes, it is judicial activism. But Ken H would say that it's good judicial activism because our guy is the one doing it.
One who misrepresents the Constitution is said not to be a "strict constructionist", not a judicial activist.
(Strictly speaking, a judicial activist is a judge that overturns legislation. I used the term loosely.)