I agree, and suggest that "not determining which side" would refer to the orientation of the barrel more so than the left or right ear. Note that the stamping on the key on the right in the pic is inverted. That suggests to me that the barrel of the key on the right was facing upwards rather than downwards as it came through the press and, given that it is unlikely that the stamp would rotate in the press, further suggests that the stampings were intended to be on the right ear of the key. Conversely, perhaps the intent was to have the stamping right-side up (readable) when holding the key in your hand. If so, then the key on the left side of the picture is the anomaly.