Kaboomed into a rock, most likely. Generally, the risk is greater the nearer one is to land.
It would be nice to see what other cargo was aboard. A pile of coins that big suggests it was a big ‘un, maybe one of the Roman grain haulers. THAT would be excellent.
Lionel Casson wrote that travelers in the know back then, if on a long Mediterranean journey, would pay for their passage aboard one of those. They were much more roomy, offered more privacy, and were much safer as well.
“Roman grain haulers.”
So that might have been payment for a delivered load of grain?