I think the separation makes sense. Scheduled meetings spread out through the day rather than grouped together and running efficiently is definitely a bad day for me.
But small, 2-5 minutes interruptions for a quick question never bothered like it seems to do with a lot of people here on HN. I can go back to my focus pretty instantly after a “quick question interruption”.
Yeah, sounds right. I think they're separated because an abundance of meetings, or just poorly scheduled meetings, can contribute to lack of focus time.
I notice that if you add the "lack of focus time" responses to that, you'd get the 3rd most significant factor, which feels closer to right to me...