Whether whoever did this was thinking as a terrorist is something that none of us know at this point, and there's not much use in speculating about it.

The essential thing about being a terrorist is to have a political motive of some kind for what you do. Terror can be carried out by a government, by an organised paramilitary group, by a cell or gang, or by an individual. The authorities naturally prefer to think in terms of centrally organised structures, because that gives a notional target, but that can be an illusion. Terrorism by individuals and small cells which may be completely out of touch with any larger organisation is perhaps a much more frightening threat.