That's what I am thinking. When you come across a coin like this, someone was saving it and it got spent for one reason or another, and so it still has original mint luster. I would guess it was sitting in a "mint set" package for 50 years and never increased in value and got spent. Often, B and M dealers buy entire collections, and coins like this just get handed out with change. Because what they are interested in are the 1909 S VDBs and 1916-D Mercs, etc. which they can make a large profit on, and these face value coins just end up in the register.
I found a 70 D a couple weeks ago. I thought the same, must have come from a set. Mine even had some nice pastel toning. Good catch, glad it was taken out of circulation before it got too jacked up.
