The substance of Roystons point is not wrong, but in the interests of absolute accuracy he could have described what he meant in different words.

I don't think he intended to argue specifically that one cannot prove a negative.

That assertion in isolation would have no bearing on the subject of the thread.

I think the context is given by the thread title and by the post to which he was responding.

His point, clearly in my view, is that if you claim that something is true, the onus is not on somebody else to prove that your claim is wrong, but on the person making the claim to give evidence to show why they have made that claim.

In this context, a newspaper claims that Sharia courts are growing in number.

How has it arrived at this conclusion? what evidence has it seen to inspire such a claim?

to expect the person asking to see this evidence to provide their own evidence that the claim is untrue is preposterous. No evidence = no basis for claim.