RJ, I (like Dave) looked into this a bit. Airborne infection is rare and does not occur naturally, but it can occur. However, something that might make you rest easier tonight is that
Clostridium botulinum (the bacteria that cause botulism) cannot grow in air according to
this site (which also happens to be from Canada). So, I don't think that the growth on the can is that bacteria. It looks like a fungus to me.