There are two rims. One on the smaller planchet when the cut blank went through the upsetting mill and formed it. One formed through the gutters in the dies that struck the planchet and formed the coin. When everything is perfectly aligned the planchet rim is swallowed-up by the die rim and the appearance is the one rim. This situation, everything wasn't perfectly aligned. Here's the evidence of the slight misalignment on the reverse, same side of the coin, just underneath the obverse separation. Note the faint dark line between the two rims running down the edge and then separating ever so slightly at the bottom-half. There's the error, in its detail...