The angler claimed that the fish was gill hooked and a bleeder, that is why he legally retained it.
I didn't interpret that the fish was hooked at the gill from the description provided, but it was simply bleeding from the gill, which we see quite often especially if a fish is deeply hooked. Catch and release mortality depends more greatly on the amount of blood loss than the length of the fight time. If a bleeding fish is released, then the mortality rate rises, depending on how much blood is lost and if or when the bleeding stops after it is released.
That being said, a bleeding fish doesn't have zero chance of surviving, it simply has less chance of surviving. It has zero chance of surviving when it is dispatched by a bonker.
I didn't think anyone would still take IGFA record that seriously in today's state of our fisheries.