As detected from the Notts List discussion, the CA website has the following croquet jargon definition listed for “Hard Banana:”
A stroke intending to make a roquet but as a result of a mistaken belief that there is a slope on the lawn is aimed away from the target ball, and misses when the ball travels in the straight line. Named after the 2017 MacRobertson shield after such a stroke by Ben Rothman who exclaimed (loudly and repeatedly) "but it was a hard banana".
This seems off to me. A shot successfully aimed to account for slope that roquets would seem to be a Hard Banana based on Rothman’s exclamation. The misinterpretation of the slope as described by the CA site definition should surely be called a Banana Mirage, right?