1975-D Nickel Mint Damage Or PMD

First post here and I'm a total newbie, except for being the daughter of an avid coin collector. If there's one thing I've picked up from my dad, however, it's to always sort through my spare change. So yesterday I came across a really curious nickel (to me at least). I don't have the greatest camera, or skills, but here it is:





So, tell me what that looks like to you. To my inexperienced eyes, it looks like it had to have happened at the mint, when both sides were being simultaneously struck. The coin is totally flat--it hasn't been distorted. The reverse side, from Monticello on up is very lightly impressed, as if whatever made the circular indentation interfered with the strike. On the obverse, the tumor sprouting out of Jefferson's head is not raised any higher than any other elements of the coin's design. That seems to me to point to a force coming from the obverse side at the same time as the indent was made on the reverse side. So that's my case for why it might have happened at the mint. What do you experienced folks think?