This was not misplaced at all. If you look at https://www.openstreetmap.org/relation/63512/history/259 you can see that the relation of the State of Maine had no Tag "Boundary". It was then added on the next update, https://www.openstreetmap.org/relation/63512/history/260, with the update description mentioning "US State Maine: boundary tag was missing on relation".
Either way, I'll resolve the note, since it no longer applies. Thank you for bringing this to my attention! Regards.