To me it looked like a brain fart, where your memory does not automatically recall for you.
When I was young; childhood into my teens, I used to have a type of social anxiety disorder, years before it was popular in medical science. I was comfortable with being among people, but interaction with some strangers would trigger a switch in my brain, between talking and thinking, causing me to stay stuck in thinking, and become sort of temporarily mute.
Some people are stuck on talk mode; don't think, with that being annoying, but not considered a pathology. But being stuck in think mode in social situations, creates pregnant pauses, which can make people feel uncomfortable. The fear of the switch activated and it becoming uncomfortable, was the primary source of my anxiety. I was often worried about the switch shutting off my voice, at awkward times, when I wanted to say something. Maybe it was a type of self censor, to avoid saying what was unfiltered, on the top of my mind; arrogant or mean.
I can sort of see Mitch, having a switch moment, which is fine among his close friends who know him, but which can become awkward to those who are not used to this, from a politician, whose living depends on talk mode.