a vistors visa they are basically tourists and would need travel insurance and could possibly charged for any treatment
That is the rule, but they are never charged as no admin department is set up to handle it, it's much less hassle and cost effective to just treat them.

When was the last time you went into a hospital they asked for your medical number and ID before they treated you? They can't even be making patients a cup of tea, cleaning the wards, or being polite.....