If you have something in mind that you want to create it's frustrating if it looks different than expected. In this case, it was a slipped pencil (the way he reacted could be my son). If that happens a second pair of eyes can be helpful and of course someone with an opinion of his own.
It sounds you had a great fun day but what I wonder is why an artist isn't able to sit still for a few minutes. Too busy gesturing? Despite of that the result is great.
An helpful second eyes is sometimes mostly needed when creating art because there are cases where the artist won’t be able to see somethings in his art by himself until he has someone else to help with it which has happened to me before, there was a time even I couldn’t come up with a title for a piece I just concluded until a friend just randomly made a suggestion and it resonated with me so much that I had to adopt it immediately
Well being an artist doesn’t change the fact that he’s also human and it’s in our nature to not be able to keep some position for long, some do a better job at controlling themselves but I believe he was just too curious as to knowing how the drawing was progressing that he ended up having to want to see and caused him to move a lot
Thank you so the thoughtful response, I really appreciate it.
And I say thank you for sharing a bit of an artist's life. A great comment!