Oops! Sorry, I saw a curved part and assumed the discussion was about a clip. I should read better next time. Either way, it still looks like
PMD to me. If the coin was missing metal on that part before the strike, from a clip or a flawed planchet or whatever, the rim around it would also be thinned out. I don't see that happening here. Blakesley effect isn't always present if the clip is small, either.
The reason why the zinc has hollowed out from the copper is because of zinc rot, which happens when the copper plating is broken and the zinc corrodes away faster than copper.