Other mistake: While asking Napoleon to pull him into town, Kip is putting on his roller blades. They live on a gravel road seen in other shots which would be impossible to rollerblade on while being towed behind a bike.
Other mistake: When Napoleon finds Trisha's picture in the yearbook, the person to Tricia's left is named Stephanie Stevens, however the picture to her left is obviously of a male. Also, the row of pictures above Tricia includes Matthew Smith, whose picture is of a female, and Taresa Sorenson, whose picture appears to be rather masculine. (00:36:05)
Chosen answer: This is never explained or referenced.