Given that they dented their call while doing the demo, it doesn't seem weird to fixate on. I think the criticism is valid, given the framing presented and the pitch used to investors.
Also, audio interfaces incur different amounts of mental load / distraction. I wouldn't be surprised if this was more distracting than just talking to a person.
I think the car dent story originally came from - https://news.ycombinator.com/item?id=45008239. As I clarified there - the dent happened before the April demo, during hackathon stress while taking out the car from parking.
But totally valid criticism about cognitive load - better example could be dog walking, cooking or screen free time.
Also, audio interfaces incur different amounts of mental load / distraction. I wouldn't be surprised if this was more distracting than just talking to a person.