You can't just distrust a single source you should have trusted, or make a single bad calculation, and end up believing in creationism or homeopathy.

You don't even need to do a bad calculation to believe in homeopathy. You just need to be in a social environment where everyone believes in homeopathy and not care enough about the issue to invest more effort into it.

If you simply follow the rule: If I live in a Western country it makes sense to trust the official government health ministry when it publishes information about health issues, you might come away with believing in homeopathy if you happen to live in Switzerland.

There are a lot of decent heuristics that can leave someone with that belief even if the belief is wrong.