They also did it with raising prices, and both did the same way. It may not have been official, but the behavior was the same either way.
That’s the thing though, because they don’t have an agreement across the city, if he and his neighbor go too high someone will undercut them. He’ll even under cut his neighbor if he thinks he can get enough more business. I’m not disputing that he’ll follow them up too. A cartel differs by manipulating the market instead of responding to the market.