Well, Nando,
It is tiny, indeed.
On the other hand, if I remember it correctly, the 1,000 year-old samples from the Egyptian period of the Fatimids were quite small and delicate as well. And the 17th c. clay hand grenades at Forchtentein Castle, Austria are of an average diameter of only ca. 10 cm.
I am about to get into contact with a real scholar on this field of hand grenades and will ask his opinion. He did research on a great number of clay and glass grenades kept in the Forchtenstein Armory. Maybe we will all know better then.
Best,
Michl