How is this recipe labeled vegan when it uses butter? Are you meant to assume substituting margerine?

I bet it would taste just fine with olive oil or coconut oil.

What I've run across in other recipe collections is groups of recipes declared vegan, kosher etc. that are evidently culled by inexact algorithms from the general collection; I would assume that happened here- if the author declare in the body of the recipe that it's vegan they probably know, but general searches often need further filtering by the user.