Your point is logical.
However, Nadler is a proven liar -- he is, after all, a liberal.
He gains nothing by admitting that the NSA can listen to any call they wish. Indeed, his side is hurt by that admission.
Consequently, it is reasonable to believe that, in this particular case, he just might be telling the truth.
He may be. Dianne Feinstein fits the same mold as he. And she says differently.
Interesting times.