Interesting. Leg 0' mutton/gigot sleeves historically weren't cut ( like this one is) in 2 pieces with a top and bottom. The cut was all in one from wrist to shoulder, with a distinctly drooping shape above the fitted lower arm. That said, the leg o' mutton sleeve could also be cut as a two pieces vertically, with an inner or under panel and an outer sleeve, like a two piece suit sleeve.
The style with the gathered puffed top and bottom ( horizontally seamed, upper and lower sections ) was also called a melon sleeve and sometimes ended at the elbow area, sometimes went fitted to the wrist.
Both types had in common big volume and an emphasis on shoulder width/height.
Due to the soft drape, small amount of volume and bicep length, I would also call this a Juliet sleeve. And a pretty effect it is.