Just experienced this today and am glad to see it's not all that uncommon. I'm also wondering if whoever did it actually laid two eggs.
We have 5 young-ish hens. Our blue-green egg layer is molting and currently not laying. The remaining 4 are (or will be) brown egg layers. 2 of them just started laying last week. So far, I've been able to tell whose egg is whose because Gertie keeps laying hers on the floor.
Eleanor has figured out the nesting boxes and lays hers in there. The 2 ladies who've yet to lay are the same age as Gertie and Eleanor, so they should be starting any time now, too.
So this morning I went out to feed them and clean the coop and was met by TWO eggs directly under the roost. Right in the poop, of course. It was hard to tell because they were frozen, but one was broken and looked like it had a soft or non-existent shell. The other one wasn't broke, but had what looked like crack lines all over it. I tossed them both in the compost, but now I'm kinda wishing I'd brought them inside the house to thaw, just to see how hard the shells were. Our ladies have crushed eggshells available all the time and all the eggs we've gotten so far have all had really hard shells.
Then later today, Eleanor laid an egg in the nesting box. SO... either Gertie laid two from the roost last night, or by some huge coincidence we have a new layer that did the same.
Eeeeenteresting.