Limo, my sister's GermEagleChowPyRusky (confirmed in a DNA test), has a fear of pumpkins and watermelons that is well documented on her blog and Youtube. Here is a clip of Limo's pumpkin surprise.
Limo, I am not sure if Riley shares your dislike of pumpkins, but you are not alone in your fear of watermelons. I was quite surprised when Riley balked at passing the watermelon in the kitchen. I normally think of her as brave and curious, so shying away from a watermelon was very unexpected and humorous.
FYI, I rarely clicker train 2 dogs together. It simply can't be done successfully except in very few cases. Riley was getting a click and treat for moving forward. Reagan was lying down during the clicks so she was being rewarded for her downs. No harm done.