It was said sarcastically in response to the interviewer's gaffe of mistaking Corey Booker for Eric Holder.
Video here: https://youtu.be/_6U1Wmq-Ems?t=65
While I agree with you, it is also true that had Trump (or any Republican) said that the howls of racism and demands for impeachment would be like none heard before. There would be marches in the streets. The point is the double standard of the left.