I've lived in CA for over 50 years. Have never seen nor heard of celery on pizza. Not suggesting you didn't come across it, only saying that it would be a rare exception.
Pizza in Rome is very different from the cheese-laden pizzas served outside of Italy, especially what's made by pizza chains. Good pizza balances tangy tomato sauce, mozzarella cheese, a yeasty, caramelized crust and a VERY light hand with toppings.
My pizzas come out between 14"-16" in diameter. I weigh the cheese (5-1/2 oz per pie) so I don't put on too much.
During a cooking class in Florence, Italy, I was floored by how little American style pizzas and other dishes resemble modern Italian cooking. Italians do not heap cheese on their foods.
As for the CNN article about pineapple on pizza being controversial in Italy? Whatever floats people's boat is ok with me. When we have pizza parties one of our most requested pizzas includes pastrami, pickles and mustard. I've never even tasted it because I don't like pastrami, corned beef, bacon, etc., but a lot of people love it.
My favorites are: Margherita, mushroom or my lemon/artichoke heart pizzas.