I know a lot of people on these boards, maybe not the ones who have responded to this post, but in general have laughed at people for the way they look or dress, even taken photos of them without them knowing. Which I personally think is a lot worse than just mentioning an incident of incorrect park attire. If you went to Disney in 2005, you would probably have a whole memory card full of my disastrous outfits! Just because a person doesn't care for fashion, doesn't make them stupid or wrong. Even women wearing high healed shoes in the parks may seem ridiculous to some people, might mean comfort and self esteem to others.
Now it is up to each individual to decide if they should cast the first stone in judging someone for making a comment, that most of you would probably found interesting (if not amusing) that someone was wearing inappropriate clothing to a park, which then malfunctioned. I don't know whether I would of laughed, but I sure as heck would have looked. I can admit that about myself.
Personally, making fun of peoples clothes in general is a sure sign that the person is feeling insecure within themselves. Take a note of how you feel on a day, and then how you judge other people, even inside your own head. If you are having a good day, you will mostly see nice outfits and pretty people. On a bad day, when insecurity bites, it will be nothing but negative. I know, I do it myself.
So yes, the comment may not have been kind, but it wasn't designed to be hurtful. No one here could say that they haven't at least thought the same about another person, thin or overweight.