If you get a complaint about somebody somebody in your organization, the first thing it is time to do is listen to both sides with your best critical thinking hat on. Going into a conversation with the accused party with the intention of getting them to do anything, before hearing their side, is an injustice.
There are cases where a warning would be a bad first step: perhaps you've only heard a report from one person, or it's not clear what happened, or you think there may be a misunderstanding. Then an opening more like "I saw some of what happened back there, can you help me figure out what was going on?" could be good, with more of a "let's find out" than a "let's change behavior" approach.
The cases that prompted me to write this post, however, were ones where a dancer had been doing a minorly harmful thing for a long time. It was very clear that they were doing the thing, and we had dozens of people who had seen them do it, including several organizers.
He also writes, specifically, that you listen to the “accused” party when taking them aside, explaining why this is important. Did you actually read this?