Everyone has a "world model". These models just differ on how much they care about various things. No one has a "world model" which literally encompasses everything about the world, that wouldn't be a model at all, it'd just be the world, much like a 1:1 map.

Also, no one has a "world model" that is purely based on experiment and reason. Everyone gets their beliefs via other people first and foremost. Some get it from few people, some get it from many people (many people can still be wrong!).

For code, you may have the model of what it does strictly from reason and experience - but probably only if you're the only author. And you can still damn well be wrong, as we all know.