It is worth noting in passing that the very church in which this attack occurred has given some land next to it to the Muslim community for the construction of a mosque. No doubt those responsible thought this would encourage mutual understanding and neighbourliness. They must be baffled as to how their church got on the Islamic State hit list. What happened? What happened is Islam's historic orthodox doctrines teach that Christians are enemies and some people acted on these teachings.
Ibrahim explains in this 15 minute audio.