Bad analogy since stamp collecting is, indeed, a hobby. It can be proved to be a hobby and someone who isn't a stamp collector can be proved to not collect stamps. Believing or disbelieving in something completely intangible and unprovable is a matter of faith since whether or not there is anything beyond the physical universe cannot be proved or disproved..
How do you prove that someone does not collect stamps? Certainly you can search for proof that they do collect stamps- but you can't really prove that someone doesn't collect stamps.
Now let us try another thought experiment.
A child is raised without any exposure to religion, without being told fairy tales, without any tales of the supernatural- with no exposure to the concept of gods or religion or faith.
That child- if she developed her own faith- would indeed have a faith. But if she didn't- she would be a clean slate- absent of any faith. She would be an atheist. She would lack a belief in god.
Just like I do.
By taking their word for