Error In Judgement Or An Ignorant Fool?

The boy got invited to his classmate's birthday party at a theme park near us. I was hesitant to let him go since the crowds, lines and all the noise might be too much for him. However, I did not want him to miss out on the social interaction outside of the school setting with his friends so I took him anyway.

The kids had a really good time. They ate together at their own table, played with each other and even sang "Happy Birthday". Afterwards, the birthday boy's mom handed out passes for the kids to use for the games and rides. 

One of the attractions was the boat ride on a mid sized, shallow pool with no more than 20 boats. It involved riding on a raft like boat while getting the people on the other boats as wet as you possibly can. He was really excited about this ride. He begged and pleaded to ride it by himself. He kept saying: "By myself Mama, by myself."

After assessing the situation and weighing out the pros and cons while we were waiting in line, I finally relented. I kept repeating the instructions to him (stay inside and seated, no standing, no hands in the water, etc.). I reviewed the rules and precautions with him over and over (and over). What I forgot to mention was that he needed to come back to the dock when called.

As you probably guessed, he did not come back with everybody else. We tried to call him back. The attendant even went after him on another boat. He just stayed out there, laughing and enjoying himself. While the attendant was so patient with him, the people on the sidelines weren't. One man in particular had a running commentary about the whole thing. I kept quiet until said man remarked that they should just let him go out there to "blast" my son to teach him a lesson. At this point, I turned to him and said: "You can't teach him a lesson. He's autistic!". Of course, what I meant was that's not the way to teach him a lesson. He retorted: "Well, IF HE'S AUTISTIC, HE SHOULDN'T BE OUT THERE." He added some addle minded reason that my son can get hurt. I think my jaw dropped at this point. I wanted to ask him as to where does he think my son should be. Should I keep him home so he can't experience life outside of its four walls? Or should I keep him locked away in a basement so he does not inconvenience anybody?I was so furious and shocked that somebody can even say such a thing that the words didn't come out of my mouth. Thankfully, he walked away mumbling before I can  do say anything to him.

My son did come back, safe but wet, after a second ride. I think that's all he wanted anyway, another turn at the ride without having to go through the line again. I reprimanded him for that. His outing got cut short as a punishment (he couldn't go to the other rides with his wet shoes anyway).

Now, I wonder, was that an error in judgement on my part? Was I wrong to let my son experience such a simple childhood pleasure? Or was that man simply an ignorant fool? What would you have done?