The highly-rated midfielder was also linked with a move to Celtic, while at Hannover.
“I’m delighted to have signed Huszti as I think he can be a top player,” said Advocaat of the 25-year-old.
“I’m surprised to hear Celtic had made him a priority because, to my knowledge, they made no offer.
“If we had not signed him, he’d have gone to Hamburg. If this is bad news for Celtic, then I’m okay with that.”