In the past, I have seen news stories in Thailand labeling all kind of ordinance as 'grenades', so when I see the word grenade in a Thai news story, I expect to see a land mine or a mortar bomb that some farmer has dug up.
However, these are real fragment grenades.
These cannot be classed in the 'self defence' bracket.
These are weapons of war, designed to create the maximum carnage.
How does an expat make the connections that he would have needed to get hold of this cache?
He must have some fantastic stories and friends who the local police, New, Zealand police and Interpol will want him to share.