There is the fact that Grusch gave sworn testimony to congress on it, he's going to prison for perjury if he's lying. Doesn't prove it, but it's more than just saying it in an interview.
People lie to Congress all the time without any consequences. That depends more on the political necessity of having a scapegoat/figure to tar and feather than the actual law.
"does the NSA collect any type of data at all on millions or hundreds of millions of Americans?"
"No, sir."
"It does not?"
"Not wittingly. There are cases where they could inadvertently perhaps collect, but not wittingly."
So, do people lie to Congress all the time? Not wittingly, but in the sense that this phrase means "absolutely yes, all the damn time."
