I think many friends of characters take their roles very seriously. And they need to seeing that one wrong slip will show up on the internet and the news. (Case in point, the infamous Tigger situation not that long ago.)
I can see the attendant not know at that time something was going on. I doubt what happened went on for a prolonged time. And pretty much anyone with a cast bubble badge on are constantly attending guests. Quite often the attendant is down a line of people to either inform or control the line. Not to mention answering questions and general guest interaction.
I can't count how many times I have asked a character attendant to trade pins with me. That is distracting. And I am sure they are constantly distracted.
Some characters are what I would consider petite in stature, and their head is the main thing one would notice. It may be difficult to even see them full body in a crowded, confined area.

I am also sure the character was pretty shocked when it initially happened. I know most would just be stunned and in disbelief at first. Although one would think they are trained for such occurrences. Which is where the not coming out of character would come in. After awhile it would just be second nature.
People do funny things when they are on vacation. Things they may not usually do. Part of a mob/show off mentality maybe.

Not to say anyone did or did not do anything. That is for the court to decide once they hear what is presented.
Adding I just started reading the article. And he was convicted. Well, there ya go...