No, I am not saying that confirmation bias will make you identify settings as kitchen sinks regardless of whether or not they are kitchen sinks.
I am saying that the designation, "fantasy kitchen sink" as you use it is not useful in the first place because, according to Brennan, a Hard Fantasy setting should be "weirder and more wonderful than you could possibly even imagine." So when you look at a setting, if it is literally realistic, it should contain phenomena that is so weird and so wonderful, you cannot even think of it. So you are not getting false positives from confirmation bias, you are getting false positives because your human brain is too limited to understand the chaos of the real world.
It's kind of like how you will once in awhile hear that movies based on true stories will tell little believable lies in place of actual events because audiences aren't willing to believe the truth. A recent occurence of this I read about is with the new movie about Tommy Wiseau