It's just a normal Kol. I've not checked the stats on it but it's named a Kol and looks like a Kol.
A Flagship is a beast of a ship, something that would take a long time to create. Something that would cost you plenty of funds and materials. Something so spectacular we can only build one.
Now this is the proper use of the name Flagship. This is the super capital ship everyone's talking about.
It's the ship you use to lead those ultra important assaults. It should come in late in the game, after lots of research. It's not something we should be likely to see in a small campaign at all, unless you seriously take it slow.
It's a good way to keep all sizes of campaigns fun. On a smaller campaign you would not get to use all ship types, but in larger ones you would. And both would be equally fun.
Atleast this is my take on the whole thing.