I think I dont have to explain much more. This is a daily ritual. Whatever I want to give her.. she want to check first. 
I am not sure if she can nose the content of the tin but she probably wants to check if it´s a tin of wed food or one of the other boxes with dried food.
Cats are just like that ! they must “know”, and decide. Like we do…
True. And it is fun to learn about the “wants” of the own cat. And also important. I like to see when my cat makes decisions. After the years I learned what she likes and what not. But I still let her decide because it might be that she likes fish.. but maybe not today. As you said.. like we are.