I call that rude.
First of all, being disagreed with is not the same as being called a liar.
Second, yes, generally speaking you don't expect someone to prove a statement was NOT made. You can only prove if it was.
But you appear to be talking about this comment: "...but when a judge rules that the flying Os vetting has been tweeted and facebooked as proof..."
The comments the judge made about things on the internet, were not offered as "proof". They weren't things he relied on to make a decision. So a statement implying he did is in fact false. It didn't happen.
He did mention those things, but that's all. He mentioned them. He did not rely on them.