Anyway, what difference does the origin of the statement make? The companies are either trying to deceive us, or they aren't. What matters is what's being done to us. We're all powerless here except to let politicians know we're unhappy, will vote against, fund EFF, etc. "Gotcha" parsing of official statements is not an important tool in this fight.
Personally I find ridiculous the notion that proud public figures will feel less ashamed technically not lying than actually bald-faced lying. Either way, you've sacrificed public credibility. So the whole discussion of "is this really a denial?" is uninteresting to me.
Assuming it the program is classified, and assuming that Zuckerberg has a security clearance, then under federal law he would potentially be eligible for the death penalty if he were to confirm the existence of the program.
And the answer is "a myriad of different phrasings could have expressed the same content. English, even encumbered by lawyers, is like that.".