It's different and here is why
The Christchurch attacker specifically targeted one mosque and his intent was to harm as many Muslim worshippers as possible.
However in Sri Lanka the terror attacks were more broad, they had two targets
A) Christian churches
B) Posh hotels full of international tourists
I saw a guy and one of his sons being interviewed on the news last night. He had lost his 19 year old son and 15 year old daughter who were at the breakfast buffet getting him some food. They were not Christians. Local people of all faiths who worked at the hotel died as well.
So blanket calling all the victims in Sri Lanka "Christian" isn't correct, even though Christians were one of the primary targets.
But in Christchurch, it's fairly safe to assume that worshippers in a mosque are Muslim. Plus the guy had a whole manifesto about why he did what he did.