Browned Butter Skillet Choc. Chip Cookie: Possible error in recipe - should there be a whole egg in addition to the egg yold??

As I was making this recipe, I noticed that the ingredient list only says "egg yolk", but the instructions mention to add "... egg and egg yolk". I got curious and checked the source recipe from DamnDelicious.net, and I noticed that it calls for a whole large egg plus an egg yolk (and it also calls for only 1/3 C granulated sugar rather than 1/2 C). I was wondering if the omission of the egg from the ingredient list was a deliberate adaptation or an error (since it's still mentioned in the instructions)? If it was a deliberate adaptation, the instructions should be revised; if an error, the ingredient list should be updated. Thanks for your attention on this!