It's nearly impossible (for me anyway) to see any detail on the coin, but what I can see suggests it being nothing more than damage.
Considering the many tens of billions of coins minted (in this country alone) and each has a near infinite number of ways it can be damaged, it would probably be best to try to post better photos. I understand this can be tough for those not familiar with imaging them, but the more you can provide the better the help we can hopefully offer. Welcome to the forum.
Still difficult to tell but acid is one method of damage. A double outline can be gained by applying the right acid to a specific area with a q-tip. The polished effect can be done with a dreamer tool and a buffer. There are a million plus ways a coin can be damaged. Yours didn't leave the Mint looking like that.