It could also have been removed from a set and put into circulation by someone who wasn't interested in the set or value, such as a kid. I've seen specimen quality coins in circulation on more than one occasion, both when I lived in Canada and here in the USA. Always makes me cringe a little and I rescue them most of the time. Some of my nicer finds include a 1909 VDB
Wheat penny (Pretty roughed up, but still lots of original luster, a 1974 PL Canada Penny, and a 1967 PL Canada penny.