With the way Hawaiian schedules interisland flights this is common. Under 30min. connection times in HNL means that you'll be on the same aircraft and have the same crew for your flight. B717 flight crews usually do 2 - 3 round trips a day between the islands, with each B717 itself being scheduled to do up to 12 cycles a day.
For those who travel from neighbor island to neighbor island there isn't always a direct flight so you have to connect in HNL. The flight attendants will make an announcement onboard after landing saying that those connecting to "Flight Number" to "Destination" may remain onboard and to give your boarding pass to the flight attendants so they can give it to the gate agents to be scanned and returned to you. It's very convenient and you don't have to deplane and board again onto the same aircraft.