OP you're confusing a (contracted) lounge that *A uses with *A or *A airline operated as said above me.
Did you notice when you entered it maybe said something like "Menzines Premium Lounge" or something like that? Probably has a bunch of other random airline placards outside the door as well?
I don't begrudge *A for being "weak" in the KLM fortress at AMS. And you're right there's lots of great places in the terminal. I like to go to the oyster bar thing and then go up to the observation deck.