I have one hen that does lay 2 eggs in one day. But this happens every 4th day. Days 1 & 2 she lays a single egg. Day 3 no egg. The next day she lays early in the morning and then again in the afternoon.
It helps to keep in mind that hens (well mine at least! lol!) never read the rule book; they don't know what they "can't" do.
It is entirely possible for a hen to lay 2 eggs in one day, happens every month or so for me and I only have 2 laying hens. Though they could of been hiding it too.