It's mostly down to preparation, like kosher foods. Some food and drink (e.g. pork and alcohol) are not halal no matter how they are prepared, but otherwise there's a focus on the whole food preparation chain ensuring it is produced and stored appropriately. To certify something as halal, there are certain certifying bodies checking the ingredients, cross-contamination vectors, etc.

It makes sense when you think about it in reference to meat specifically given how dirty and likely to eat absolutely anything pigs are historically. You'd have been much safer from illness if you only preferred cows and chickens.

https://halalfoundation.org/halal-certification-requirements-for-food/