Reading the history of the place is this any significant difference than usual? I would suspect there's an uptick in death, but it's an island with a million dead bodies that is regularly used to bury unclaimed bodies.
With such a small island and so many bodies, I would suspect that these are typically buried in such a utilitarian fashion. That is, a "mass grave".
1500 burials on that island a year on average over the last decade. Five a day? I have to imagine they are buried together like this typically. Probably don't bury them five at a time. Even if you do burials twice a week you're still going to be putting 15 or 20 people into the ground at once consistently.