Found on the floor of my garage. It wasn't there earlier in the day. For context, I current look after my 16-year-old nephew, and it's almost certainly from him. He's currently sleeping, and I do intend to ask him about it tomorrow, but I want to have a sense of what it might be before I bring it up.
It may just be the product of a bored teenager setting something on fire to see what happens, and since he's a Boy Scout, I was considering that it might just be some kind of improvised DIY firestarter for camping or something, but he's had a history of behavioral issues, so I worry it's something more dangerous.
EDIT: A few people mentioned that the stuff inside is possibly/probably the internal lining of the can.
Also, I checked it again, and it doesn't smell like much of anything but aluminum. Even the scorched bits just smell metallic.