So, you've just hit on a weakness of the legal "reasonable person principle" and, possibly, the reason Google decided to settle this case. By settling, they've

So, you've just hit on a weakness of the legal "reasonable person principle" and, possibly, the reason Google decided to settle this case. By settling, they've left the legal question of what a "reasonable person" should expect here open. If someone else wants to sue later over this term or some related term maybe having a different layperson meaning, they can but they're back to square one: new case, new facts, no precedent. Had Google dragged this out, and the Court concluded that a "reasonable person" believed "incognito" meant something other than what every tech-head has understood it to mean for the past sixteen years... The industry would have been in for a world of hurt.