The nationality of the forum is irrelevant. We're discussing applications to a UK university using the language which is spoken in the UK. If people think that 'you don't know what you're talking about' is polite it's only fair to warn them that their potential professors and fellow students at Oxford are unlikely to agree.
Ever heard of context? I assume people will behave differently towards professors and fellow students in an everyday class setting as opposed to towards a random anonymous person needlessly spreading a false rumor on an internet forum where everybody is already living on a knife-edge because of all the stress that comes with applying. If that person had done but 5 minutes of research on Google he/she would have easily found that the rumor is not true, but instead, the person chose to post such an unsettling message on a forum where everyone is already living in a state of anxiety.
Now, I am not condoning the fact that the reaction was blunt (because it was), but if you had an elementary capacity for empathy you would understand why that person reacted the way he/she did to the spreading of a needlessly confusing and badly researched opinion.
Interesting that you've singled out my post for your little injunction about what can and cannot be discussed. I can only assume you either approve of the preceding sarcasm and nastiness or just didn't fancy picking a fight with the bullies. Personally, I don't like to see people subjected to rudeness for making a simple mistake, it isn't conducive to the supportive atmosphere which your subsequent posts suggest you would also like to cultivate.
Then maybe you shouldn't have responded in such a condescending and arrogant manner. Maybe if you had replied in a way that didn't treat the OP like a badly behaved child you would have succeeded in truly cultivating a supportive atmosphere.