Paparazzi at Tenjune got confused Tuesday when Sean Kingston strolled in. The R&B star was at the club to celebrate the launch of his new album, “Tomorrow” — but photographers, seeing a cake that had been brought in for the occasion, kept wishing Kingston a happy birthday. “It became a joke to the point where he just started saying, ‘Thanks!’ ” laughs a source. Kingston ended up doing three songs before hanging out with Russell Simmons, Lil’ Jon and Rick Ross.