"Terrorism is a term used in its broadest sense to describe the use of intentionally indiscriminate violence as a means to create terror or fear, in order to achieve a political, religious or ideological aim. It is used in this regard primarily to refer to violence against civilians or non-combatants." (Wikipedia).
The attacker said he wanted to kill all Muslims. To me, that seems to fit the definition well enough. As far as I can tell the violence was intentional; it was used against unknown individuals indiscriminately; and its aim was not concerned with robbery, personal revenge, seeking advantage or for any other reason except a hatred of a religious group.