It is indeed a mint error; the term you're looking for to describe it is "broadstrike". That's when the two dies that usually smash together to make a coin both work fine, but the collar die that is supposed to hold the coin in place and impart the reeding on the edge is missing.
Broadstrikes are usually off-centre a little bit, since there's no collar present to hold the coin in the proper place. The term "off-centre broadstrike" usually refers to coins so far off centre that bits of the design are missing (which is not true in this case).
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