We could say "Oh, this means there were almost 10 illegal weapons at every raid", but, they were not evenly distributed, just like raiding every house in a dodgy estate will turn up a lot of illegal items, but most of them will be centered in a small % of properties, so, yeah, for 2500 raids, most of them will have returned nothing.
Not almost 10 illegal weapons at every raid. More than 10 raids for every illegal weapon.
Otherwise I agree with you they're likely not to have been evenly distributed, so you can assume there were far more than 10 raids for every raids that produced one or more weapons.
They found 230 illegal weapons. That's not what I call nothing...