PAX WAS INADVERTENTLY LEFT ON BOARD ACFT DURING REFUELING.

Narrative

OUR FIRST FLT TOGETHER WAS FROM BOS TO PVD AND AFTER A QUICK TURN IN PVD A CONTINUATION TO EWR WAS PLANNED. UPON REACHING PVD; ATC INFORMED US OF A 50 MIN ATC DELAY TO EWR. I ADVISED THE FO TO HAVE ALL PAX DISEMBARK WHILE I INFORMED THE STATION AND ORDERED FUEL. MY FO MADE THE ANNOUNCEMENT AND PROCEEDED WITH HAVING ALL OF THE PAX DISEMBARK FOR THEIR COMFORT AS WE ALL PLANNED TO WAIT INSIDE THE TERMINAL UNTIL OUR NEW EDC ARRIVED. I SECURED ALL SYS ON THE ACFT; LOOKED TO THE BACK OF THE PLANE; PUT ON MY UNIFORM JACKET; RETRIEVED SOME PAPERWORK FROM MY FLT BAG; ASKED THE FO ABOUT SOME COMAT WE WERE CARRYING; AND THEN PROCEEDED TO LEAVE THE PLANE; CLOSE THE DOOR; AND GO INTO THE TERMINAL. WE SAW THE FUELER SVC THE ACFT; WAITED OUR ALLOTTED TIME; AND THEN PROCEEDED TO RE-BOARD THE ACFT FOR OUR FLT. MY FO PROCEEDED TO BOARD THE PAX AS I OBTAINED LAST MIN WX AND DISPATCHER INFO. AS WE TAXIED OUT; MY FO MADE REF TO A PAX AND I TOLD HIM I WAS NOT CLR ABOUT WHAT HE WAS TRYING TO TELL ME AND TO WAIT UNTIL WE WERE AT CRUISE. AT THAT TIME; HE INFORMED ME A PAX DID NOT GET OFF THE ACFT IN PVD; WAS ON THE ENTIRE TIME DURING OUR GND DELAY AND REFUELING AND WAS UNABLE TO GET OUT. HOWEVER; HE (THE PAX) SAID IT WAS NO PROB AND HE JUST WANTED TO READ ANYWAY.