a. That was a tank, not artillery. I have no idea why would they write that as shelling (even in the sources mentioning it’s a tank, and even putting a picture of it).
b. If the shelling refers to the airstrikes than Gaza’s officials says it hit a number of Hamas positions and they had not received any reports of injuries.
c. The target is to attack the same individual, if possible, but if not, Israel sees Hamas as the ruling entity, and retaliates against its military posts. In this case, they fired on a post watching the place where the IED was located.
d. The people killed were Islamic Jihad (confirmed by them).