Basque Powder

Yesterday I bought a jar marked “Basque Powder” at a local farmstand. The label indicates it contains only pepper powder. But I was expecting it to contain other things as well, such as powdered tomato, onion and Mediterranean herbs. Is there a convention regarding seasoning blend versus just Espellette powder?

I really like the taste–starts out spicy-mild and then builds significant heat. I can see using this in/on all sorts of things.