He's definitely familiar with the 'notion' or he wouldn't be commenting on it. Maybe he meant to say he has no knowledge of anyone being blocked from testifying, which would also probably be incorrect.
My beloved daughter-in law asked me about this today. She is from Northern Italy, and speaks English well, but has a hard time with the “nuances” of our language.
I did my best to explain the difference between “not knowing” about something, and being familiar with it.
Best I could come up with is asking if she “knew” her her next door neighbors (yes).... was she “familiar” with them (no).
But, most of the low-information voters probably don’t get the difference either. It is so easy to lie with words. Bill Clinton taught us that.
It all depends on the meaning. I wonder if the loyal White House Correspondents get the difference?