Talked to his Vet today on the phone. He said watch him this weekend see if it happens again, come in Monday if so.
Said to always be concerned since vomitting is not normal. Said most times it's explainable, like ate something, etc. but do not brush it off if it happens several times.
So, I will be watching.
It's like a puddle of saliva and white foam, not the kind like when his tummy was upset with the stomach bug going around.
Let me know what your Vet say.