I was not able to view the video. so I'm not responding with the benefit of seeing that. However, there is reson for you to be reassured if the several MD's (incl. the gastro specialist) you consulted are OK about what they witnessed.
Well I have showed 3 peds the video and they say they are not worried about it. I also showed his GI the video and he said he wasnt worried about seizures either. So no referall leaves me stuck.
I did notice this morning that he was wincing while swallowing his finger puffs. I wonder if his throat is sore, maybe that would explain the shiver..
It would be wise to arrange evaluations with both a pediatric neurologist and a pediatric gastroenterologist. Teething would not explain what you are observing.