Even thin glass won't usually shatter on light impact; you have to give it a hard, sharp smack to make it explode, eg. throwing it against a hard surface. Just look at beer bottles as comparison (and those are made much thinner than hand-blown glass could get with reasonable surety); they don't even break most of the time unless thrown with a fair amount of force (angle of impact also helps, considering the shape is not spherical). Additionally, glass containers of all kinds are much harder to break when filled, since the material within will help drastically in absorbing shock.