if it was gold plated you can still buy gold plated pennies, quarters, half dollars, etc https://merrickmint.myshopify.com/collections/24k-gold-plated-coins-1 plus high school experiments. a variety of reasons to find a gold plated, silver plated or what ever plated coin.
but I like @Collecting Nut explanation which is more likely. you can see different wear from the brighter spots to the less bright spots. Different wear like that probably indicated something was covering parts of it. See the surface differences