Potter knew? Had Dumbledore told him? Draco knew he was being paranoid - but he also didn't trust any of them, and why should he? So to extend it, why should he trust Dumbledore to keep his secret at all.
His arm itched.
"I don't know what you're on about, Potter." He sounded as sure of that as he sounded of anything else. If he was going to show his hand, it wouldn't be to Potter. Being caught crying last year was a fluke, and a disgrace.