The ciphers are public. What the NSA really wanted was the size of file headers, special markers, etc -- so they could skip over the fluff and home in on the juicy stuff. I gave up nothing that would put the product or users at risk.
And just because a cipher is public does not mean that there does not exist a side channel in the implementation of the ciphers or a mistake in your usage of them.
And just because they have the source code, doesn't mean they couldn't get it from reverse engineering the binary. I have not seen a binary that was completely resistant to reverse engineering yet.
Likely he was just saving them time.
That's an enormous assumption based on zero evidence. The only resource the NSA is limited by is time. Money and man power (up to diminishing returns) are effectively limitless.
They were trying to skip a step, but there's absolutely no reason to believe they could have (and would have) done without through reverse engineering the binary. The NSA guy implied time was the major factor, and wanting the source certainly implies that was the case.