What is he thinking?! I would not help after getting fired!
It probably isn't under his control. He can be subpoeanaed. In any case, he got a nice severance package and I think is technically still a "consultant" (i.e. on a paid leave until he doesn't have any more insider knowledge that a competitor can use) and so has contractual obligations to Apple.
On a personal level, Samsung was found to have copied "his" ideas (iOS was under his control at the time) so he may want to see them lose.