1903 Cent In Mysterious Condition

So my grandpa gave me this coin several years ago when he was getting rid of some of his collection, and the shiny 1903 Indian Head cent was part of it. When he gave it to me it was in a small gray box (idk if he received it in that box). It is worn as normal from circulation ([LIBERTY] on headdress is missing, few details on wreath & arrows, etc.)

I just want to know if this coin is shiny on its own, or if it has been processed or treated with something to make it look that way. I imagine if it had circulated into the 1950s (47-57 yrs) it possibly could have stayed clean until a collector took it, because I can still and just recently found a few cents from the late 60s and early 70s in a roll together, which were about 43-50 years old and in very similar condition; slightly worn, but very shiny. The surface of the reverse of this coin does look like it's starting to aquire the grayish-orange dull color that many copper cents from the late 60s to 1982 can be found with.

If anybody can debunk this coin to be reprocessed or treated and not original, I'll appreciate it, although a bit disappointed.