The article is very clear in the mechanism: he posits companies are “blindly” colluding by using third party price information to inform their decisions on their own pricing. This isn’t “collusion” because they’re not the picking up the phone to each other to discuss price fixing. They’re allowing a third party to tell them what others are charging and “coincidentally” decide that they’d like to charge that, too.

If this fits the legal definition of a cartel and price fixing, I can’t say. I’m not a lawyer nor do I know what US law says on this matter. However, it’s fair to say there’s a bad smell to the whole affair.