So all the candidates at one event answering questions from a moderator and given a chance to respond to each other isn't a debate? Sounds like one to me. The key thing here seems to be if they are on stage at the same time.
In addition to them not all being on stage at the same time, it sounds like each candidate gets multiple questions (for a total of probably ~4 minutes or something), before they move on to the next one. Then they cycle back through the candidates again with some kind of followup questions.
So I guess it's like a slow motion debate? You ask everyone about 3 or 4 questions at a time before everyone else can respond? Wherea in a normal debate, it's one question at a time?
But yeah, this was clearly designed to push the limits of the "no unauthorized debates" rules.