How is Streetlight Manifesto considered Ska compared to real Reggae Ska like The Charmers?

You Have Ska which is Reggae Ska like the Charmers then you have a jump to a wierd Ska mix like Streetlight and Reel Big Fish. Wouldn't that be like a mix between Swing/Jazz and Punk Rock. The only thing that sounds like rock and raggae is Sublime. how does that work?