Like I said, everything about Batman is PIS if you follow the mere human rule. A world famous party socialite isn't a master MA with multiple degrees etc etc AND fights crime on a nightly basis....
But we accept that...so where do you draw the line?
And agree with all of Darkseids feats. But its precisely because HE is capable of that....that he believes Batman would also be capable of it. Like I said, he wasn't presented with a fiendish riddle to solve. He just believed that Batman would do it. And tbh, nothing Batman did (or Darkseid knew of humans) led DS to believe he was faking.