Jim's experience with this false-memory episode is just quite like any other. Memory get edited and changed through a period of time because you interrept it how you would've liked to see it and how it suited you. Ultimately false memories are created the same way that real memories form, so it is hard to distingish each other from wrong to right. Many hypothesis can be obtained on what may have happened to Jim that day, but the main ones are a common disease like dementia or he could have been altered by hypnosis.
The event may have been plausible meaning that it could have been easily altered because of a event that happened during