I think it is not a type of insect gall.
I do not think this is viral.
It is not bacterial either.
But it is probably fungal.
I guess --- the pathogen is a species of Taphrina (Ascomycete) This genus produce naked asci.
子囊菌門, Taphrinomycetes, 外囊菌綱, Taphrinales, 外囊菌目, Taphrinaceae, 外囊菌科, Taphrina deformans, 有效學名. 子囊菌門, Taphrinomycetes, 外囊菌綱
你可以参考 桃縮葉病Taphrina deformans