Well, crossing fingers that we are in the clear. He managed to get food in him and keep in down including some of his regular kibble by the end of the day. Just got up this morning he's almost back to his normal routine. Went out pee, gave him a small amount of kibble with chicken, and now he's back in bed with DH.
So, as the vet thought, is was probably gastroenteritis? He didn't have any diarrhea leading up to the vomiting. Still waiting on his first poop since starting to eat again.
Either way, thank you to the Lab mojo!