Zach knew he didn't know everything. Even once stuff got written down and stuff, he wouldn't unless he studied it a long time, despite living through it. His memory wasn't the best most of the time. That was why, back in school, Zach had asked . Yes there had been the strong desire to just know everything about everyone (he still gossiped with many of the ladies in the Ministry), but honestly, Potter made claims, and Zach had wanted to know the truth.
That was some time ago now, and what mattered...some things simply couldn't be changed, no matter what Harry said. Many people looked up to Harry, loved Harry, all that whatever silly nonsense. It's what it felt like to Zach. But Harry had never changed Zach's life for the better or really changed him much at all directly. Causing Cedric's death was the main way he'd affected Zach at all. Cedric had changed Zach. Colin had changed Zach.
Entering the cafe with Potter, Zach wondered how much Harry had been there before. Zach knew this area quite well. London was his city and had been his city for a while. Plus, having worked at the Ministry for a few years now, he knew a lot of the places to get lunch. "Cedric would have saved the world, if he could," Zach commented, still as unhappy as before.