In Harry Potter and the Order of the Phoenix we see Hermione start this passage talking about how Harry was good at Defense Against the Dark Arts
"You were the only person last year who could throw off the Imperius Curse completely, you can produce a Patronus, you can do all sorts of stuff that full-grown wizards can't, Viktor always said ---"
Ron looked around at her so fast he appeared to crick his neck; rubbing it, he said, "Yeah? What did Vicky say?"
"Ho ho," said Hermione in a bored voice. "He said Harry knew how to do stuff even he didn't, and he was in the final year at Durmstrang."
My question is what exactly did Harry know how to do that Victor Krum didn't? More importantly even if Harry did know how to do some stuff Krum didn't - how would Krum know this? I can't think of anything that occurred during the Triwizard Tournament that would give Krum any reason to say that Harry knew how to do stuff even he didn't know how to do.