It appears that the coin was struck normally then found itself back in the minting press for a second weaker strike.
Obverse has a weaker inner circle from the reverse imprinted on it and you can see "Half Penny" rotated by about 230 degrees over Georges bust. You can see the reverse legend overstruck on the obverse legend.
Reverse has the obverse legend struck over, which has obliterated some of the lettering
Sandwiched between two other pennies in a roll and somehow they were squished? I really have no idea, but that's what I'm picturing in my head. Not sure two similar metals could imprint on each other though.
Hmmm, actually I think my idea would leave impressions of the words, not raise them up as it appears in your photo.