That's what I thought, but I went back to that scene and only came up with the screenshots above
I thought it was when Clarke was flipping through it with him, but when I go to that scene she only looks briefly at the picture of the dropship he drew, with the 100 markers beside it then she goes back downstairs.
But I remember her saying something like 'what is this?' and looking at the bigfoot, so she must have looked through the book with Bellamy again, but for some reason I can't find that part