I don't see a video but the pictures don't tell me anything other than you have a cute kitten. Be aware that your vet is not a breed expert, he's a health expert

And tabbies can have the lighter spots on the back of the ears (although generally more dramatic in cats with exotic cat heritage like Bengals and Savannahs) and even classic tabbies can have spots on bellies. Kittens generally have larger ears than they will as adults, in breeds like the Bengal they hope the kitten "grows into" their ears, when of course us Savannah folk hope the ears keep growing with the cat!
Unfortunately there is no DNA test for Serval heritage....so it is really guesswork, maybe more of an educated guess when a person has seen a LOT of pictures of cats including Savannahs. We in Savannah Rescue do a lot of breed identification for other rescues, for shelters etc...
It would be good to see more pics of his face looking at the camera and his body. Being so thin when you found him it might be some time to really see his body type as right now I'm guessing he's really thin and hence might well fill out in the coming weeks.
He is a very lucky kitten to be found and now have a great new home! You are right it is unlikely that a savannah would be dumped like that especially in a state that up until recently didn't allow Savannahs hence there were not any breeders there.
At the end of the day, you can decide his history and nobody can prove you wrong! If you want him to be a Savannah or Savannah mix...