The whole open mouth thing is all about doing anything for clicks in a desperation to get more views. It is used by many YouTubers as a way of getting people to click. You see the thumbnail and think, “Oh wow, this must be exciting and interesting, look at how shocked this guy looks.” Then you click, and it’s just some old guy mansplaining everything with his mentally challenged married girlfriend.
I could totally see Spencer searching "how to get more clicks" on Google, and the first thing on the list was "shocked facial expression thumbnails."