According to you and others who feel the same way. Unless something is written in the law book, nobody is right or wrong when it comes to other issues--spanking, CIO, co-sleeping, etc.
That mother did what she felt she needed to do to protect her child. Maybe the OP's husband seemed creepy to her. Maybe her gut told her to ask that question.
If an MDC mama came on here and said:
"We went to the water park and DS had to go to the bathroom. I sent him into the men's room by himself. He was in there for an awfully long time. I kept asking if he was okay and he said he was. Out of nowhere, a man walked out. I didn't think anyone was in there. It scared me. I yelled out the DS "did someone touch you?" to which he replied "no".
I think I embarrassed the guy and I feel really bad! But the vibe I got told me something wasn't right. I had a really bad feeling in my stomach and I called out to my son. It was a horrible experience. I feel really bad and need a hug. What would you have done?"
The responses might be a mix of "you were wrong" and "you were right" but I think it's safe to say that many responses would be "you were just following your gut. You always listen to your gut."
Nobody is right or wrong according to us. We all do what we feel we need to do
As for the "I kept asking if he was okay"? Again - really off. If you're worried, ask what's taking so long, or call him back and talk to him. Standing there asking repeatedly if he's okay isn't going to accomplish anything. She obviously didn't think she could trust the response, for whatever reason, so why bother asking? (I'm not blaming her for not trusting the response. If she really thought the OP's dh was a pervert, maybe she thought he had a knife or something. Who knows? But, if she doesn't feel that standing outside, repeatedly saying, "are you okay?" accomplishes anything, there's not much point in doing it.)
And, yes - it's still wrong to publicly accuse someone of being a pervert, because he was using a bathroom. We can split hairs over whether or not it was an accusation, but she was definitely expressing suspicion, based on nothing but his gender, in a very public way. When we get to an "OMG - did someone (obviously meaning a specific person) touch you?" simply because a man walks out of a men's bathroom, things are going haywire. The people in the picnic area don't know that the only reason she said it was because he was in the bathroom at the same time as her son...and many, many people subscribe to the ridiculous notion that "where there's smoke, there's fire".