In the "Harry Potter" series, Harry's statement about his dad and friends not being at Hogwarts 50 years ago is accurate. The reference to 50 years ago is related to Tom Riddle's time at Hogwarts, who later becomes Voldemort. Voldemort attended Hogwarts in the 1940s, approximately 50 years before the events in the books. Harry's parents, James Potter, and his friends Sirius Black, Remus Lupin, and Peter Pettigrew, attended Hogwarts during the 1970s.


The confusion arises when Harry discovers the Half-Blood Prince's potions textbook and realizes that it belonged to Severus Snape. Snape, however, was at Hogwarts during the same time as Harry's parents, not 50 years ago. The Half-Blood Prince moniker comes from Snape's mixed blood status. So, while Harry's father and friends weren't at Hogwarts when Voldemort was a student, Snape was present at the school during their time, making him the Half-Blood Prince.


In summary, Harry's dad and friends were not at Hogwarts 50 years ago when Voldemort was a student, but Snape, who was at Hogwarts during their era, turned out to be the Half-Blood Prince.