There is a lot of unknown information in this event, as well as some variables. The RCI ship was set to leave at 8:30pm and the Carnival ship not until 10pm. The RCI ship left 3 hours early and the Carnival ship 4 hours early. Given that passengers are required to be checked in 90 minutes prior to scheduled departure, this means there was a 90 minute change for RCI passengers and a 2.5 hour change for Carnival.
So - were people actually flying to SJU with windows that tight? Or were some of them already checked in and had then left the ship to explore San Juan? Or were others already on the island but had not checked in at their respective ships? Only a fool would be flying down to SJU in the late afternoon when the requirement is to be onboard the ship at 7pm for RCI and 8:30pm for Carnival.
We'll never know the specific breakdown, but I'd like to know how many had checked in but were stranded when the ships left early. The news story makes it sound like everyone was still flying in and I don't think that is the case.