How can you lose a boat and not know?

Looking at mainland Panay Island from atop the hills of Mararison Island.
Photo from Byajayro

As written in Panay News. 

The speedboat was three to four kilometers from the shoreline of Barangay Aras-Arasan at the time. 

All the passengers, except Dable, were able to hold onto the speedboat when it flipped. According to Jaromay, the speedboat hit Dable on the head.

Tan and Barrentos, on the other hand, swam for more than two hours to the shoreline to seek help until fishermen saw them, Jaromay added.

“Mayor Tan went on board a pump boat and went back to where the boat capsized and rescued his friends and visitors,” the police chief said./PN

I am someone who can't swim and has been to Mararison which is why this news is hitting me a little wrong. 

Good thing I read this only after coming home from 6 hours, each way, on an outrigger to Jomalig Island, or else that would really work me up.

Two hours? The victims on the boat are the ones who notified the shore there is a boat that tipped over. 

What's boat traffic like the day of the incident? What port did the mayor take off from? Maybe it was outside the usual traffic. There's a local tourism office at Culasi before you hop on a boat for Mararison. 

ABSCBN credits photo to MDRRMC Sebaste, Antique

I know you can't see a small boat all the way to the island from Culasi,  it's just that from mainland to Mararison is about a 15 minute travel. 

The attached picture at the very top of this post by a travel blogger is taken from a high point in the hills of Mararison. Travel time should really be short.

How do you lose a boat and not be aware the soonest?