Well, we now know that a catfish can reach at least 9 feet and 650 lbs, and it's not likely that that one particular catfish was the THE largest.
In my opinion it's not weird to think that huge catfish exist in the US also. When you think about it, how much time do humans spend hanging around the bottom of deep fresh water? Also, it's only natural that when people re-tell the story it happened in their local lake or river.
Anyway, if a diver for the Thailand Dam Authority tells me that he was checking the base of a dam and he saw a giant catfish I guess I wouldn't have any reason to doubt him.
