At this point we don't know.
What is known is that the "Sunday SDA" leadership is dogmatic about their decision for Sunday, and have done considerable to discourage and put down the "Saturday SDA" members. But that doesn't mean they would stoop to a criminal act.
So why the building of the Independant SDA Church (Saturday Sabbath people) burnt down we don't know, at this point.
The independant SDA Church, was independant before the dateline change occured. It is quite a large organization on the islands, with headquarters in Australia, and unlike regular SDA church there, they keep the Sabbath, not Sunday.
There is only fear that foul play may have been involved, and if so it would definitely show unchristian character, but at this point we do not know, and therefore need to refrain from accusations.