OK, so I realise I'm probably going to get flamed for this, but this is my opinion:
Peanut allergies can be lethal. If you are the parent of a small child with a peanut allergy, then I would imagine that you teach that child of the dangers of peanuts, and to avoid them at all costs. So, a small child sees peanuts in the ground in Fantasyland and - quite wisely - recognises that they are to be avoided. A small child doesn't know that they are probably fake - why would he/she? Isn't everything in WDW made to look real to children? The child's reaction is completely sensible and rational, and may well save his/her life one day.
Even as an adult, who's trained yourself to look for peanuts in unusual places, you may think logically that they are fake, but would you be willing to bet your child's well-being - maybe even life - on it? If not, then what do you do? You find out by asking a cast member, or calling Disney. You can then be reassured, and in turn reassure the child that those particular peanuts are make-believe and that they can enjoy Fantasyland.
All of which is a logical and reasonable response for people that are in a unique situation. No-one in that thread was "up in arms" about having peanut details in the concrete. I cannot imagine what it would be like to be a parent of a child with a peanut allergy; I do not pretend to know what they're going through. But if I was in that position, I think I would probably be devastated to be mocked for those actions.