These two quotes seem to be in conflict - both from GoF:
Moody had told them all during their last Defence Against the Dark Arts lesson that he preferred to prepare his own food and drink at all times, as it was so easy for Dark wizards to poison an unattended cup.
The stranger sat down, shook his mane of dark gray hair out of his face, pulled a plate of sausages toward him, raised it to what was left of his nose, and sniffed it. He then took a small knife out of his pocket, speared a sausage on the end of it, and began to eat.
Why didn't Moody prepare his own food? Why did he eat the school's sausages? Was sniffing the food a means of detecting poison?