For what it is worth, I spoke to a local SXM friend who happens to be a long time and 2nd generation licensed taxi driver with a full sized GMC/Chevy van.

His understanding (he was not working at the time but since he knows other taxi drivers, I am sure he got close to accurate information) is as follows:

A SXM taxi driver had prearranged tours for MANY people on this ship as I guess there was a large contingent he had connected with. The SXM taxi driver then enlisted some fellow licensed taxi drivers and also at least one UNLICENSED driver to get this large group around. The group was enjoying their tour while in multiple taxi vans and were also partaking in the party atmosphere while touring. It is his understanding the very large group (multiple vans) had stopped in Marigot for more refreshments when the young and unlicensed taxi driver of the van in question backed up so his group could converse with another group. At this point he neglected to put the van in park and when the tour was ready to move on, he accelerated while still in reverse and went into Marigot harbor. I was also told many of the vans were filled beyond capacity (by a few people) as the large group wanted to stay together and they could not secure enough vans.

While it appears to have been a licensed taxi van, the young driver may not have been licensed, was inexperienced and according to my friend, had no business behind the wheel.