Headline is a bit click-baity from variety or whoever.
What the judge has essentially decided is that, in theory, a trailer could contain false advertising. I would imagine there was a motion to dismiss based on the argument that the trailer is a creative work entitled to first amendment protection, and the judge rejected that argument. The judge held that it is commercial speech, and if false commercial speech is provided very limited protection.
There's a far bridge to cross from there to a movie trailer actually being found to consist of false advertisement in a case like this. From there, (generally speaking I don't know the nuances of Chicago law), a person, or more likely a group of people, would have to prove that the trailer was the primary, or at least a significant, factor in them deciding to see the movie, that it was reasonable for them to rely on the trailer, that the specific element in the trailer induced them to see the movie, without that element the movie is substantively a different expecience, that the viewer's interpretation is correct etc etc.
TL:DR version, the judge just gave the people an opportunity to make their case, or at least not have it dismissed on first amendment grounds (or the state law equivalent). They still actually have a huge hill to climb, and I'd be pretty shocked if they actually win this case. Honestly, the law firm who was hoping to cash in on this should have really been patient and waited for a much better set of facts.