In my experience Christmas and Easter are two of the busiest times at churches, with many only really going to church around those times. So a distinction between regular attendees and, let's say "part time" attendees, isn't an outrageous notion.
I do like to see that you're getting triggered by the use of "Easter worshipers" though.
Why do you like to see me getting triggered? I'm wondering why there was specific use of that language rather than simply stating that Christians were attacked during Easter celebrations, I mean it's obviously to avoid stirring anti-Islamic sentiment, but who told them to do it?