User blog comment:BashfulWolfo/Grey Mullet/@comment-26865028-20190323055449

That's a 1 in 100 chance, so nice catch!

On topic, I also agree that it's a neat little addition to the game, if you look at it this way, it's a similar mechanic to shinies in the Pokémon universe - Sometimes it'll turn up when you search hard enough, or like how I did, you'll come across it by complete random chance ¯\_(ツ)_/¯