He was hoping he might get away without introductions or small talk. Too much to hope for, apparently.
"Malfoy," Scorpius told her, mustering the best smile he could manage. "Scorpius Malfoy," he tacked on as he put the sickles in the register box and closed it.
He decided to keep it at that rather than acknowledge she was his great Aunt. Best to let her steer the direction of the conversation, lest he slip up and say something completely tactless.