What would you do? Naughty behavior

Here’s the type of scenario. What would you do?

At a public gathering for children that meets once a week. It’s generally a quiet environment but it is one hour a week and a special time for young kids and families(so during that time not as quiet as usual)

My child(3.5 years old) joined this group late(so everyone else knows eachother already). But he gets along with everyone and is very sociable. A few times, we have attended when other children were behaving “badly” like running around, not listening, chasing others, etc. So this might be an excuse I am making up to try to justify his behavior, but I think that he believes that it was this special time is supposed to be like. Basically, he doesn’t know better. But he doesn’t behave like that at home or anywhere else. So I really think it’s his association with this particular event because his first experience(and subsequent each time) has been this way. However, today, these other kids weren’t there and it was apparent that his behavior was like their’s even in their absence.

Here’s what I did:

I was trying to appear less annoyed than I really was because I am amongst other parents and a child development/teacher, etc. Usually, I would shut the behavior down right away. But because I was amongst all of these other, seemingly, very patient and tolerant adults, I just tried to correct his behavior. His behavior was up and down, not aggressive or mean natured. But disruptive and pushing other kids boundaries. He calmed his behavior alittle but still not listening as well as he usually does. I eventually was at the point that I just kept distracting him. We finish with the event and left. I explained to him why another child wanted to get away from him even though she was very playful and engaging with him from the start. He was crossing her boundaries, grabbing her arm, trying to chase her, etc. He seemed to understand. I told him that next week if he behaves the same way that we will get up and leave. I explained he must sit, listen and follow the lead of one of the other children(alittle older and a great example for the appropriate behavior in that setting).

So my natural reaction would normally be to get up and leave. I am very patient but not so much when it comes to this type of behavior especially when he isn’t listening. However, on the other hand, I understand that he probably believes it’s the appropriate behavior because he has seen other kids behave that way and not have any consequences. But I won’t tolerate it. Should I discuss this with the leader of the group ahead of time or just up and leave if his behavior warrants it? (It’s a very small group and it is intertwined with other group activities we are a part of and that she is the leader of) I won’t give empty threats so I’ve already told him that next week if his behavior is that way we will leave. We will also talk about it a lot up until then.

So am I right or am I expecting too much? What would you do?