My guess would be, new mold or no trolls.
These guys got toes, fingers, nose and ears. I know minifigs usualy haven't got that but for a large figure it would proapbly need that.
Also I think it would be abit odd to make a set and not include all 3 trolls... And a set with 3 large figures seems abit much...
Also I would hope lego is better than reusing molds that almost fits.