Not tossed - ejected. These are inserted into the vent (touch hole) on the piece. When the piece is fired the primer is literally blown out of the vent and can fly 50 - 100 feet in the air and land yards away from the cannon.
In the photo from a reenactment night firing demonstration you can clearly see the smoke and flame shooting from the vent.
View attachment 1673691
Also, your primer is in remarkable condition. You might want to see if there were any reenactments in the area where you found this. After the 150th CW commemorations, it's not unusual to find lost reenactor gear. I know first hand about losing gear. I lost my Enfield bayonet in the woods at the 150th Battle of the Wilderness. I suppose someone in the future will be very pleased with that find.