If that is an actual photo of the mine, then my suspicions have been correct. There is no hole for a primer/fuse/detonator/etc on the top and it is a solid casing all around. Probably with a screw on the bottom, so that it can be filled with sand, and perhaps a wire carrying handle. Most Engineers, Crewmen (especially Assault Troopers), Pioneers, and Infanteers would be familiar with these practice mines in the last 50 or so years. Many Reserve Units had them also. They were held by many units in limited numbers for training purposes. Some may have also gone AWOL over the past 60 years, pilfered by 'collectors'. Guess someone decided they didn't need them in their 'collection' anymore. Not a very bright way to dispose of them. Someone could have been seriously hurt in the confusion, or in the actual distruction of them by the use of real explosives.
I suppose the point should be made to anyone who is a "collector" that they should turn their stuff into the proper authorities, or if small enough, put them in one of the "Amnesty Boxes" found on most CF Bases. Ammo Techs can attest to the numbers of cases each year where they are called to 'dispose of' someone's collection of live and/or inert ammo from previous years/wars.
Was this another case of someone who shouldn't be in the gene pool? Guess, we will never know.