I'm thinking that Phaedra probably got that information from her husband. It's the kind of thing that comes up when you talk about your childhood and your life at home. Food would be a natural subject, since a lot of comforting memories associated with it. I don't think there are lots of canned foods in prison, since the sharp can edges can be, easily, turned into weapons. Lord only knows they figure out how to turn things into cutting weapons that you never would think about; I can't see the prisons making things that easy for them.