...you will almost certainly not see this, of course, but it might make me feel a bit better.
I'm really sorry that the lady snapped at you and your son (who has ASD?) when you tried to get down the side of the dog agility pen, but it was for your son's own safety. There were dogs tethered on the other side of the fence who had just been doing training runs, who were in their working environment and who were therefore very het-up, excitable and unpredictable. They started barking and growling when you approached but you persisted in moving closer to them.
The lady snapped because she was worried that the boys were going to touch the dogs through the mesh (as they were trying to do) where they could easily have been bitten, as well as worried for the welfare of her own dogs who were becoming very wound up, especially when one of the boys started to make barking noises at them.
Lots of Loud Parenting ensued, "my son has a mental disability" etc. - well, all the more reason to supervise him closely as he then made several attempts at opening the gates into the pen which contained loose working dogs. When you approached me I did try to explain why she'd snapped and why it was important that the boys not enter the pen, as well as reassuring you that you were next in the queue, but you seemed quite aggressive by that point and I gave up when you started demanding to be provided with shade while waiting two minutes for a free training session. I held my tongue at the "not all disabilities are visible" rant because I have SEN myself.
I just... gah, I don't even know who is being unreasonable here. Anyway. I'm sorry you got snapped at and felt you had to defend yourself like that.