You can't count the fan base even in one city of 50 000 people, even less in the whole world.
333 million football fans? What a number

It looks like they did everything to make it look like they counted those fans one by one. They don't say around 300 mil, but they say 333 millions.
I'm a Juve fan. If you ask my wife who does she support she will tell you Juve too, even though she knows nothing about Juve, she never watches matches, doesn't know a single player.
Now, my wife is like 3/4 of those "333 million United fans". I was talking about fans like you and me, not "fans" like my wife.