I haven’t seen any source suggesting it was a pen. Several sources, such as https://www.aap.com.au/news/police-powers-bolstered-as-terror-attack-probe-widens/, describe the weapon as a “flick-knife”. Other sources say that the bishop victim was “seriously injured”, and the assailant was injured in the attack and his own finger was sliced off with the knife.

I think you are right that no one died, but wrong that the weapon was a pen - this was a serious attack with an actual knife.