I would not trust that site at all. To start with there is only one breed and that is Turkey. There are many different varieties of turkeys. There final blurb about heritage turkeys making the claim that there are 13 recognized breeds is just an outright lie. There are many more than 13 varieties of heritage turkeys but the APA only recognizes 8 varieties.I do not know who or what this site is about...quick google search and the names all sound familiar to me ( I am like you and don't know much)
https://www.roysfarm.com/turkey-breeds/
The turkey that they are showing as a Blue Slate turkey is appears to be a Lilac.
A good site to learn about heritage varieties is Porter's Rare Heritage Turkeys.