Saying that that statement is a fact is presumptive, and it is being asserted without any evidence.
It isn't a fact at all, which is why i used quotes around the word 'fact'.
As an example, if I ask you "What evidence might one present to prove what the temperature is outside"
You could say to me "Well, i could go outside with a thermometer, measure the temperature, and that would be evidence to show what temperature it was outside" Because the question that is being asked is a question of fact, there is some sort of possible relevant evidence to demonstrate its truth or flasehood.
but if i ask you the same question about demonstrating the applicability of a law, there is no way to prove or disprove it (at least, no way that isnt argumentative and therefore self-referential). Regardless of whether its true of false, when i ask you 'how can one prove that a law is applicable', there is no way to answer the question. Because the question is not a question of fact.