I am sure there are others on this site more qualified to answer your question, but I will give you my take.
First of all, the Bighorns on Antelope Island as well as the Stansburys, and Newfys in Utah, are of the Californian Bighorn subspecies. They typically have smaller horns and smaller bodies than the Rocky Mountain Bighorns in other units, although Boone and Crockett does not recognize the difference. So while that ram is a very nice Cali ram, his score does not stack up high against bigger Rocky rams from other units. I do however suspect that he was one of the larger rams on the Island and a very respectable Ram trophy.
In much of the sheep world, there is a very strong unwritten rule to try to kill the oldest rams on the mountain, thus maintaining the integrity and stability of the herd. While old rams may not be the prettiest or even the highest scoring, they are the most valued trophy to many of us. It a code the rest of the hunting world would do well to adhere to.
So, while that ram was apparently not impressive to you, I thought he is a dandy trophy to be proud of. I can't speak for the lucky hunter about why or how he chose that one, only that I am sure he is very proud of it.
I will say his cape looked a little battered, and I am sure there is a story there as well.