I don't get the comments about the big surprise either. This was Bolelli's first US HC match, Haider-Maurer is a decent challenger player and Bolelli is still far from where he once was. People tend to think he is already on his level of 1,5 year ago, because he won a challenger off late, but no by far, especially not on HC.
He should have stayed in Italy to play clay challengers, at not travel to the US solely to play these qualis without any preparation.
Haider-Maurer also hasn't been playing on hard, and in fact as far as I can recall has never done anything remotely impressive on the surface. He's also much less talented than Bolelli. It was an easy match-up for Simone. I am not saying he was a shoe-in to qualify, but someone of his talent should be able to battle through as a weak section of the draw as he found himself in here.
I also don't know what comments about a 'great surprise' you are referring to (other than gulzhan's wow), as no one described this as a great shock.