Interestingly, this one is one of those cases where it is totally up to the judge or juries thoughts on reasonability. They have always disclaimed that incognito only removes traces of your traffic on the local computer. They also explicitly stated that third-parties would not be hindered by or actively prevented from tracking you. Though the point of confusion or getting in trouble here is that they (Google) are both simultaneously, the browser writer of the functionality guaranteeing discretion, but also reaping value from tracking the traffic. This would fall under my personal metric of sketchy, contraindicative/regulatorally problematic behavior.
If the layman, despite that disclaimer is nevertheless found reasonable to expect functionality to be one thing, but what is delivered is something else than that stated, it could fall under deceptive practices under the FTC Act. If I understand the gist of this lawsuit correctly. Not a lawyer, but read a legal research book once.