Probably going to get buried here.
Look, I totally get that this is a joke, but this is also very very wrong, and it is conveying the wrong message about musicianship. It will stop people from entering the zone while playing if they take what he's saying as legit, educated information. It's kind of toxic, and for those that want a genuine definition (Nearly a decade of playing, applying for a doctorate program in the fall if the $ comes through for daddy)
This guy is tarnishing a real phenomenon that happens when you are completely focused on music. To focus on people's faces is completely indicative of someone that does not compose or play pieces that are extremely close to themselves. I get that this is sort of a parody, but it is super common to hear when people see someone playing from an intensely focused emotional grounding.
When someone writes a profound song, a lot of times it happens at an emotional high or low. Sometimes it is simply characterizing a part of their life, almost like taking a picture. It is their expression. They are living, breathing human beings expressing themselves, and the sounds are a process of that. It is an art form. When you see someone's face move naturally while they are playing, when their eyes show emotion, when the muscles in their neck spasm...
These are signs that someone is fully connected with the music. In the same way that their fingers flow freely out of control, so does their physiology as a whole. This guy is more or less turning one of the most beautiful parts of becoming a musician -- becoming the music -- into another uninformed version of a joke video that only demonstrates he probably hasn't ever written an instrumental on the day his grandma died and let go while he played it. Musicians from every instrument do this, and this video is just a product of a general misunderstanding. You want to listen to the guitarists that let go when they play. You want them to be playing with their physiology.
But nah. Just a joke vid. Wouldn't want to talk about musicians that wrote songs the day they lost a loved one or finally made it. Nah, let's just talk about their faces...doesn't matter if it spreads the wrong message right? Right. Cuz I'm not gonna let that be the end of this.
tl;dr fuck you i don't write tl;drs