Japanese WW2 bomb found in a couple's yard in Missouri

I suppose this might be Fortean in nature but a couple in Missouri found a Japanese bomb--apparently, a grenade--from WW2 buried on their property.  It was still live.  The wife dug it up while gardening and showed it to her husband.  He started to clean it up and they saw Japanese writing on it.  She went online to try to match it up to something and it came back a possible bomb.  She yelled to her husband to leave it alone and they called the cops who took it away and detonated it.  It probably would have killed the husband had it gone off while he was cleaning it.  Then again, it could have killed the wife when she pulled it out of the ground.  It was very unstable after all these decades.  So, the question is, of course, how in the hell did this thing end up buried in a yard in Missouri?  Nothing you can come up with really makes sense.  A Japanese spy put it there?  Why?  An American soldier returned from the war with a live bomb and buried it there??  Why?  Shohei Ohtani's great-great grandfather threw it so hard that it flew over the ocean and landed in Missouri?  I thought perhaps a Japanese-American internee hid it there but there were no internment camps in Missouri.  Seven states had them: California, Arizona, Colorado, Wyoming, Idaho, Utah, and Arkansas.  So who brought this bomb to Missouri and dropped it in the dirt and left it there? 

 

www.msn.com/en-us/news/us/missouri-couple-discovers-live-world-war-ii-era-japanese-bomb-in-their-yard/ar-BB1goJRQ