As xXScytherXx said, not everyone is a medical student. And just because you have the knowledge doesn't mean that you should think that everyone who doesn't know is a fool.
Besides, you don't know what age and time the park owner grew up in. There was a time when HIV was a scare, and no one knew anything about it. Perhaps the park owner grew up in this time, and that prejudice still lives inside of him, despite what knowledge has been gained. I know people who dislike certain cultures because of the time period they grew up in. It might be that the same could be said for the park owner. You grew up in a time when knowledge is present about HIV and could be taught to others.
The park owner was acting out of the best interest of the general public. As an owner of a public place, he has the duty to protect those who use his services. When a problem is brought to his attention he has to deal with it as he sees fit with the knowledge that he has. Yes, the knowledge might be limited. This is done in all sorts of services that cater to the public.
If he knows NOTHING about diseases, then why is he correct in deciding which precautions to take?
There are loads of people around him that could easily decide what to do (thanks for making me repeat myself though).
He's the voice of authority at the park. Who else are the employees of the park going to listen to? He's not going to let the pool boy make a decision that affects the park and its customers. The park owner is the boss of the park, and he is the only one to decide what is safe for the park and those who use its services. If you are going to say that a owner of a business has no say in how that business should be run, then you need to work in public service occupations.
People are biased about a lot of things. One reason for this bias is a lack of education. Another reason is because of the time period that the person grew up in. There are many reasons for prejudices to be formed in people.
Ah, but oh well. My main problem with this whole story is the article itself. It was written mainly to get pity for this family. The part about the love of trains, the part about the father only have months to live, and all the mentions of innocent children were just tossed in to gain pity and to make you feel for this family.
I sometimes hate being in a debating mood. :<