Ken, that means nothing as the top of the fuze with the delay primer corrodes away but the fuze threads with the primer inside can still be there. We find them often that way. You're right with inert. When the top is gone moisture gets in and kills the inner primer.
Another indicator (if it is a pineapple) is the rust. Life grenades usually look like new when coming out the ground. The only ones rusted are the ones without fuze. I guess the chemicals of the powder are responsible for that.
Western part of Germany. Years ago we got sometimes 4-5 every time we're out. Back then you found them complete with ring. Now corroded more they often come out the way like yours. (Still not sure if it is one. Soak it in apple cider vinegar for some weeks...) Last harvest a farmer had over 20 in his potatoe harvester....
It is super corroded but it looks suspiciously like an Mk2 grenade you should probably call you're local police and they can coordinate with an EOD response team in your area.