If I remember this position correctly, the assertion is that pure math and mathematical physics are really the study of the organizing principles by which the intellect interprets and makes sense of the world. Rather than being properties of an exterior phenomenal world, these disciplines describe the rules of the mind itself. The phenomenal world necessarily appears to conform to these principles because these principles dictate the terms of perception itself. Much as we can’t imagine a sense other than those we’re given, it’s impossible for us to perceive a reality that doesn’t meet the terms imposed by the intellect. We can look at these principles apart from empirical data because they are, in effect, our own intellect.